man mimedefang-filter (Formats) - Configuration file for MIMEDefang mail filter.

NAME

mimedefang-filter - Configuration file for MIMEDefang mail filter.

DESCRIPTION

mimedefang-filter is a Perl fragment which controls how mimedefang.pl disposes of various parts of a MIME message. In addition, it contains some global variable settings which affect the operation of mimedefang.pl.

CALLING SEQUENCE

Incoming e-mail is handled as follows:

1) A temporary working directory is created. It is made the current working directory and the e-mail message is split into parts in this directory.

2) If the file /etc/mail/mimedefang-filter.pl defines a Perl function called filter_begin, it is called with no arguments. Any return value is ignored.

3) For each leaf part of the mail message, filter is called with four arguments: entity, a MIME::Entity object; fname, the suggested filename taken from the MIME Content-Disposition header; ext, the file extension, and type, the MIME Content-Type value. For each non-leaf part of the mail message, filter_multipart is called with the same four arguments as filter. A non-leaf part of a message is a part which contains nested parts. Such a part has no useful body, but you should still perform filename checks to check for viruses which use malformed MIME to masquerade as non-leaf parts (like message/rfc822). In general, any action you perform in filter_multipart applies to the part itself and any contained parts.

Note that both filter and filter_multipart are optional. If you do not define them, a default function that simply accepts each part is used.

4) After all parts have been processed, the function filter_end is called if it has been defined. It is passed a single argument consisting of the (possibly modified) MIME::Entity object representing the message about to be delivered.

DISPOSITION

mimedefang.pl examines each part of the MIME message is examined and chooses a disposition. Unless otherwise indicated, the dispositions should be called only from filter and not filter_begin or filter_end.

The available dispositions are:

accept
The part is passed through unchanged.
accept_with_warning
The part is passed through unchanged, but a warning is added to the mail message.
drop
The part is deleted without any notification to the recipients.
drop_with_warning
The part is deleted and a warning is added to the mail message.
replace_with_warning
The part is deleted and instead replaced with a text message.
defang
The part is passed through unchanged, but its MIME type and filename are changed to values which make social engineering attacks harder.
quarantine
The part is deleted and a warning is added to the mail message. In addition, a copy of the part is saved on the mail server in the directory /var/spool/MIMEDefang and a notification is sent to the MIMEDefang administrator.
bounce
The entire e-mail message is rejected and an error returned to the sender. The intended recipients are not notified.
discard
The entire e-mail message is discarded silently. Neither the sender nor the intended recipients are notified.

CONTROLLING RELAYING

You can define a function called filter_relay in your filter. This lets you reject SMTP connection attempts early on in the SMTP dialog, rather than waiting until the whole message has been sent. Note that for this check to take place, you must use the -r flag with mimedefang.

filter_relay is passed two arguments: $hostip is the IP address of the relay host (for example, "127.0.0.1"), and $hostname is the host name if known (for example, "localhost.localdomain") If the host name could not be determined, $hostname is $hostip enclosed in square brackets. (That is, ("$hostname" eq "[$hostip]") will be true.)

filter_relay must return a two-element list: ($code, $msg). $msg specifies the text message to use for the SMTP reply, but because of limitations in the Milter API, this message is for documentation purposes only---you cannot set the text of the SMTP message returned to the SMTP client from filter_relay.

$code is a literal string, and can have one of the following values:

'REJECT'
if the connection should be rejected.
'CONTINUE'
if the connection should be accepted.
'TEMPFAIL'
if a temporary failure code should be returned.
'DISCARD'
if the message should be accepted and silently discarded.
'ACCEPT_AND_NO_MORE_FILTERING'
if the connection should be accepted and no further filtering done.

Earlier versions of MIMEDefang used -1 for TEMPFAIL, 0 for REJECT and 1 for CONTINUE. These values still work, but are deprecated.

In the case of REJECT or TEMPFAIL, $msg specifies the text part of the SMTP reply. $msg must not contain newlines.

For example, if you wish to reject connection attempts from any machine in the spammer.com domain, you could use this function: 

sub filter_relay {
	my ($ip, $name) = @_;
	if ($name =~ /spammer\.com$/) {
		return ('REJECT', "Sorry; spammer.com is blacklisted");
	}
	return ('CONTINUE', "ok");
}

FILTERING BY SENDER

You can define a function called filter_sender in your filter. This lets you reject messages from certain senders, rather than waiting until the whole message has been sent. Note that for this check to take place, you must use the -s flag with mimedefang.

filter_sender is passed four arguments: $sender is the envelope e-mail address of the sender (for example, "<dfs@roaringpenguin.com>"). The address may or may not be surrounded by angle brackets. $ip and $name are the IP address and host name of the SMTP relay. Finally, $helo is the argument to the SMTP "HELO" command.

Inside filter_sender, you can access any ESMTP arguments (such as "SIZE=12345") in the array @ESMTPArgs. Each ESMTP argument occupies one array element.

filter_sender must return a two-to-five element list: ($code, $msg, $smtp_code, $smtp_dsn, $delay). $msg specifies the text message to use for the SMTP reply. If $smtp_code and $smtp_dsn are supplied, they become the SMTP numerical reply code and the enhanced status delivery code (DSN code). If they are not supplied, sensible defaults are used. $delay specifies a delay in seconds; the C milter code will sleep for $delay seconds before returning the reply to Sendmail. $delay defaults to zero.

(Note that the delay is implemented in the Milter C code; if you specify a delay of 30 seconds, that doesn't mean a Perl slave is tied up for the duration of the delay. The delay only costs one Milter thread.)

For example, if you wish to reject messages from spammer@badguy.com, you could use this function: 

sub filter_sender {
	my ($sender, $ip, $hostname, $helo) = @_;
	if ($sender =~ /^<?spammer\@badguy\.com>?$/i) {
		return ('REJECT', 'Sorry; spammer@badguy.com is blacklisted.');
	}
	return ('CONTINUE', "ok");
}

As another example, some spammers identify their own machine as your machine in the SMTP "HELO" command. This function rejects a machine claiming to be in the "roaringpenguin.com" domain unless it really is a Roaring Penguin machine: 

sub filter_sender {
  my($sender, $ip, $hostname, $helo) = @_;
  if ($helo =~ /roaringpenguin.com/i) {
    if ($ip ne "127.0.0.1" and
        $ip ne "216.191.236.23" and
        $ip ne "216.191.236.30") {
          return('REJECT', "Go away... $ip is not in roaringpenguin.com");
    }
  }
  return ('CONTINUE', "ok");
}

As a third example, you may wish to prevent spoofs by requiring SMTP authentication when email is sent from some email addresses. This function rejects mail from "king@example.com", unless the connecting user properly authenticated as "elvisp". Note that this needs access to the %SendmailMacros global, which is not available in filter_sender until after a call to read_commands_file. 

sub filter_sender {
        my($sender, $ip, $hostname, $helo) = @_;
        read_commands_file();
        ### notice: This assumes The King uses authentication without realm!
        if ($sender =~ /^<?king\@example\.com>?$/i and
            $SendmailMacros{auth_authen} ne "elvisp") {
                return('REJECT', "Faking mail from the king is not allowed.");
        }
        return ('CONTINUE', "ok");
}

FILTERING BY RECIPIENT

You can define a function called filter_recipient in your filter. This lets you reject messages to certain recipients, rather than waiting until the whole message has been sent. Note that for this check to take place, you must use the -t flag with mimedefang.

filter_recipient is passed nine arguments: $recipient is the envelope address of the recipient and $sender is the envelope e-mail address of the sender (for example, "<dfs@roaringpenguin.com>"). The addresses may or may not be surrounded by angle brackets. $ip and $name are the IP address and host name of the SMTP relay. $first is the envelope address of the first recipient for this message, and $helo is the argument to the SMTP "HELO" command. The last three arguments, $rcpt_mailer, $rcpt_host and $rcpt_addr are the Sendmail mailer, host and address triple for the recipient address. For example, for local recipients, $rcpt_mailer is likely to be "local", while for remote recipients, it is likely to be "esmtp".

Inside filter_recipient, you can access any ESMTP arguments (such as "NOTIFY=never") in the array @ESMTPArgs. Each ESMTP argument occupies one array element.

filter_recipient must return a two-to-five element list whose interpretation is the same as for filter_sender. Note, however, that if filter_recipient returns 'DISCARD', then the entire message for all recipients is discarded. (It doesn't really make sense, but that's how Milter works.)

For example, if you wish to reject messages from spammer@badguy.com, unless they are to postmaster@mydomain.com, you could use this function: 

sub filter_recipient {
	my ($recipient, $sender, $ip, $hostname, $first, $helo,
            $rcpt_mailer, $rcpt_host, $rcpt_addr) = @_;
	if ($sender =~ /^<?spammer\@badguy\.com>?$/i) {
		if ($recipient =~ /^<?postmaster\@mydomain\.com>?$/i) {
			return ('CONTINUE', "ok");
		}
		return ('REJECT', 'Sorry; spammer@badguy.com is blacklisted.');
	}
	return ('CONTINUE', "ok");
}

INITIALIZATION AND CLEANUP

Just before a slave begins processing messages, mimedefang.pl calls the functions filter_initialize (if it is defined) with no arguments. By the time filter_initialize is called, all the other initialization (such as setting up syslog facility and priority) has been done.

If you are not using an embedded Perl interpreter, then performing an action inside filter_initialize is practically the same as performing it directly in the filter file, outside any function definition. However, if you are using an embedded Perl interpreter, then anything you call directly from outside a function definition is executed once only in the parent process. Anything in filter_initialize is executed once per slave. If you use any code that opens a descriptor (for example, a connection to a database server), you must run that code inside filter_initialize and not directly from the filter, because the multiplexor closes all open descriptors when it activates a new slave.

When a slave is about to exit, mimedefang.pl calls the function filter_cleanup (if it is defined) with no arguments. This function can do whatever cleanup you like, such as closing file descriptors and cleaning up long-lived slave resources. The return value from filter_cleanup becomes the slave's exit status.

If filter_cleanup takes longer than 10 seconds to run, the slave is sent a SIGTERM signal. If that doesn't kill it (because you're catching signals, perhaps), then a further 10 seconds later, the slave is sent a SIGKILL signal.

CONTROLLING PARSING

If you define a function called filter_create_parser taking no arguments, then mimedefang.pl will call it to create a MIME::Parser object for parsing mail messages.

Filter_create_parser is expected to return a MIME::Parser object (or an instance of a class derived from MIME::Parser).

You can use filter_create_parser to change the behavior of the MIME::Parser used by mimedefang.pl.

If you do not define a filter_create_parser function, then a built-in version equivalent to this is used: 

	sub filter_create_parser () {
		my $parser = MIME::Parser->new();
		$parser->extract_nested_messages(1);
		$parser->extract_uuencode(1);
		$parser->output_to_core(0);
		$parser->tmp_to_core(0);
		return $parser;
	}

EXTENDING MIMEDEFANG

The man page for mimedefang-protocol(7) lists commands that are passed to slaves in server mode (see "SERVER COMMANDS".) You can define a function called filter_unknown_cmd to extend the set of commands your filter can handle.

If you define filter_unknown_cmd, it is passed the unknown command as a single argument. It should return a list of values as follows: The first element of the list must be either "ok" or "error:" (with the colon.) The remaining arguments are percent-encoded. All the resulting pieces are joined together with a single space between them, and the resulting string passed back as the reply to the multiplexor.

For example, the following function will make your filter reply to a "PING" command with "PONG": 

sub filter_unknown_cmd ($) {
    my($cmd) = @_;
    if ($cmd eq "PING") {
        return("ok", "PONG");
    }
    return("error:", "Unknown command");
}

You can test this filter by typing the following as root: 

md-mx-ctrl PING

The response should be: 

ok PONG

If you extend the set of commands using filter_unknown_cmd, you should make all your commands start with an upper-case letter to avoid clashes with future built-in commands.

REJECTING UNKNOWN USERS EARLY

A very common mail setup is to have a MIMEDefang machine act as an SMTP proxy, accepting and scanning mail and then relaying it to the real mail server. Unfortunately, this means that the MIMEDefang machine cannot know if a local address is valid or not, and will forward all mail for the appropriate domains. If a mail comes in for an unknown user, the MIMEDefang machine will be forced to generate a bounce message when it tries to relay the mail.

It's often desirable to have the MIMEDefang host reply with a "User unknown" SMTP response directly. While this can be done by copying the list of local users to the MIMEDefang machine, MIMEDefang has a built-in function called md_check_against_smtp_server for querying another relay host:

md_check_against_smtp_server($sender, $recip, $helo, $server, $port) This
function connects to the SMTP server $server and pretends to send mail from $sender to $recip. The return value is always a two-element array. If the RCPT TO: command succeeds, the return value is ("CONTINUE", "OK"). If the RCPT fails with a permanent failure, the return value is ("REJECT", $msg), where $msg is the message from the SMTP server. Any temporary failures, connection errors, etc. result in a return value of ("TEMPFAIL", $msg).

The optional argument $port specifies the TCP port to connect to. If it is not supplied, then the default SMTP port of 25 is used.

Suppose the machine filter.domain.tld is filtering mail destined for the real mail server mail.domain.tld. You could have a filter_recipient function like this: 

sub filter_recipient
{
    my($recip, $sender, $ip, $host, $first, $helo,
       $rcpt_mailer, $rcpt_host, $rcpt_addr) = @_;
    return md_check_against_smtp_server($sender, $recip,
					"filter.domain.tld",
					"mail.domain.tld");
}

For each RCPT TO: command, MIMEDefang opens an SMTP connection to mail.domain.tld and checks if the command would succeed.

Please note that you should only use md_check_against_smtp_server if your mail server responds with a failure code for nonexistent users at the RCPT TO: level. Also, this function may impose too much overhead if you receive a lot of e-mail, and it will generate lots of useless log entries on the real mail server (because of all the RCPT TO: probes.) It may also significantly increase the load on the real mail server.

GLOBAL VARIABLES YOU CAN SET

The following Perl global variables should be set in mimedefang-filter:

$AdminAddress
The e-mail address of the MIMEDefang administrator.
$DaemonAddress
The e-mail address from which MIMEDefang-originated notifications come.
$AddWarningsInline
If this variable is set to 0, then all MIMEDefang warnings (such as created by action_quarantine or action_drop_with_warning) are collected together and added in a separate MIME part called WARNING.TXT. If the variable is set to 1, then the warnings are added directly in the first text/plain and text/html parts of the message. If the message does not contain any text/plain or text/html parts, then a WARNING.TXT MIME part is added as before.
$MaxMIMEParts
A message containing many MIME parts can cause MIME::Tools to consume large amounts of memory and bring your system to its knees. If you set $MaxMIMEParts to a positive number, then MIME parsing is terminated for messages with more than that many parts, and the message is bounced. In this case, none of your filter functions is called.

By default, $MaxMIMEParts is set to -1, meaning there is no limit on the number of parts in a message. Note that in order to use this variable, you must install the Roaring Penguin patched version of MIME::Tools, version 5.411a-RP-Patched-02 or newer.

$Stupidity{" NoMultipleInlines" }
Set this to 1 if your e-mail is too stupid to display multiple MIME parts in-line. In this case, a nasty hack causes the first part of the original message to appear as an attachment if warning are issued. Mail clients which are not this stupid are Netscape Communicator and Pine. On the other hand, Microsoft Exchange and Microsoft Outlook are indeed this stupid. Perhaps users of those clients should switch.

The following global variables may optionally be set. If they are not set, sensible defaults are used:

$AddApparentlyToForSpamAssassin
By default, MIMEDefang tries to pass SpamAssassin a message that looks exactly like one it would receive via procmail. This means adding a Received: header, adding a Message-ID header if necessary, and adding a Return-Path: header. If you set $AddApparentlyToForSpamAssassin to 1, then MIMEDefang also adds an Apparently-To: header with all the envelope recipients before passing the message to SpamAssassin. This lets SpamAssassin detect possibly whitelisted recipient addresses.

The default value for $AddApparentlyToForSpamAssassin is 0.

$SyslogFacility
This specifies the logging facility used by mimedefang.pl. By default, it is set to "mail", but you can set it to other possibilites. See the openlog(3) man page for details. You should name facilities as all-lowercase without the leading "LOG_". That is, use "local3", not "LOG_LOCAL3".
$WarningLocation (default 0)
If set to 0 (the default), non-inline warnings are placed first. If you want the warning at the end of the e-mail, set $WarningLocation to -1.
$DaemonName (default " MIMEDefang" " )
The full name used when MIMEDefang sends out notifications.
$AdminName (default " MIMEDefang Administrator" " )
The full name of the MIMEDefang administrator.
$SALocalTestsOnly (default 1)
If set to 1, SpamAssassin calls will use only local tests. This is the default and recommended setting. This disables Received, RBL and Razor tests in an all or nothing fashion. To use Razor this MUST be set to 0. You can add 'skip_rbl_checks 1' to your SpamAssassin config file if you need to.
$NotifySenderSubject (default " MIMEDefang Notification" " )
The subject used when e-mail is sent out by action_notify_sender(). If you set this, you should set it each time you call action_notify_sender() to ensure consistency.
$NotifyAdministratorSubject (default " MIMEDefang Notification" " )
The subject used when e-mail is sent out by action_notify_administrator(). If you set this, you should set it each time you call action_notify_administrator() to ensure consistency.
$QuarantineSubject (default " MIMEDefang Quarantine Report" " )
The subject used when a quarantine notice is sent to the administrator. If you set this, you should set it each time you call action_quarantine() or action_quarantine_entire_message().
$NotifyNoPreamble (default 0)
Normally, notifications sent by action_notify_sender() have a preamble warning about message modifications. If you do not want this, set $NotifyNoPreamble to 1.
$OpenAVHost (default 127.0.0.1:8127)
Host used for OpenAV daemon calls within message_contains_virus_openantivirus and entity_contains_virus_openantivirus unless a host is provided by the calling routine.
$CSSHost (default 127.0.0.1:7777:local)
Host and port for the Symantec CarrierScan Server virus scanner. This takes the form ip_addr:port:local_or_nonlocal. The ip_addr and port are the host and port on which CarrierScan Server is listening. If you want to scan local files, append :local to force the use of the AVSCANLOCAL command. If the CarrierScan Server is on another host, append :nonlocal to force the file contents to be sent to the scanner over the socket.
$SophieSock (default /var/spool/MIMEDefang/sophie)
Socket used for Sophie daemon calls within message_contains_virus_sophie and entity_contains_virus_sophie unless a socket is provided by the calling routine.
$ClamdSock (default /var/spool/MIMEDefang/clamd.sock)
Socket used for clamd daemon calls within message_contains_virus_clamd and entity_contains_virus_clamd unless a socket is provided by the calling routine.
$TrophieSock (default /var/spool/MIMEDefang/trophie)
Socket used for Trophie daemon calls within message_contains_virus_trophie and entity_contains_virus_trophie unless a socket is provided by the calling routine.

FILTER

The heart of mimedefang-filter is the filter procedure. See the examples which came with MIMEDefang to learn to write a filter. The filter is called with the following arguments:

$entity
The MIME::Entity object. (See the MIME::tools Perl module documentation.)
$fname
The suggested attachment filename, or "" if none was supplied.
$ext
The file extension (all characters from the rightmost period to the end of the filename.)
$type
The MIME type (for example, "text/plain".)

The filename is derived as follows:

o
First, if the Content-Disposition header has a "filename" field, it is used.
o
Otherwise, if the Content-Type header has a "name" field, it is used.
o
Otherwise, the Content-Description header value is used.

Note that the truly paranoid will check all three fields for matches. The functions re_match and re_match_ext perform regular expression matches on all three of the fields named above, and return 1 if any field matches. See the sample filters for details. The calling sequence is: 

	re_match($entity, "regexp")
	re_match_ext($entity, "regexp")

re_match returns true if any of the fields matches the regexp without regard to case. re_match_ext returns true if the extension in any field matches. An extension is defined as the last dot in a name and all remaining characters.

A third function called re_match_in_zip_directory will look inside zip files and return true if any of the file names inside the zip archive match the regular expression. Call it like this: 

	my $bh = $entity->bodyhandle();
	my $path = (defined($bh)) ? $bh->path() : undef;
	if (defined($path) and re_match_in_zip_directory($path, "regexp")) {
	    # Take action...
	}

You should not call re_match_in_zip_directory unless you know that the entity is a zip file attachment.

GLOBAL VARIABLES SET BY MIMEDEFANG.PL

The following global variables are set by mimedefang.pl and are available for use in your filter. All of these variables are always available to filter_begin, filter, filter_multipart and filter_end. In addition, some of them are available in filter_relay, filter_sender or filter_recipient. If this is the case, it will be noted below.

%Features
This hash lets you determine at run-time whether certain functionality is available. This hash is available at all times assuming the detect_and_load_perl_modules() function has been called. The defined features are:

$Features{"SpamAssassin"} is 1 if SpamAssassin 1.6 or better is installed; 0 otherwise.

$Features{"HTMLCleaner"} is 1 if Anomy::HTMLCleaner is installed; 0 otherwise.

$Features{"File::Scan"} is 1 if File::Scan is installed; 0 otherwise.

$Features{"HTML::Parser"} is 1 if HTML::Parser is installed; 0 otherwise.

$Features{"Virus:FileScan"} is a copy of $Features{"File::Scan"}.

$Features{"Virus:OpenAV"} is provided for completeness and is currently always 0. Set it to 1 in your filter file if you have OpenAntiVirus.

$Features{"Virus:FPROTD"} is currently always 0. Set it to 1 in your filter file if you have F-Risk's FPROTD scanner.

$Features{"Virus:SymantecCSS"} is currently always 0. Set it to 1 in your filter file if you have the Symantec CarrierScan Server virus scanner.

$Features{"Virus:NAI"} is the full path to NAI uvscan if it is installed; 0 if it is not.

$Features{"Virus:BDC"} is the full path to Bitdefender bdc if it is installed; 0 if it is not.

$Features{"Virus:NVCC"} is the full path to Norman Virus Control nvcc if it is installed; 0 if it is not.

$Features{"Virus:HBEDV"} is the full path to H+BEDV AntiVir if it is installed; 0 if it is not.

$Features{"Virus:VEXIRA"} is the full path to Central Command Vexira if it is installed; 0 if it is not.

$Features{"Virus:SOPHOS"} is the full path to Sophos sweep if it is installed; 0 if it is not.

$Features{"Virus:CLAMAV"} is the full path to Clam AV clamscan if it is installed; 0 if it is not.

$Features{"Virus:AVP"} is the full path to AVP AvpLinux if it is installed; 0 if it is not.

$Features{"Virus:AVP5"} is the full path to Kaspersky "aveclient" if it is installed; 0 if it is not.

$Features{"Virus:CSAV"} is the full path to Command csav if it is installed; 0 if it is not.

$Features{"Virus:FSAV"} is the full path to F-Secure fsav if it is installed; 0 if it is not.

$Features{"Virus:FPROT"} is the full path to F-Risk f-prot if it is installed; 0 if it is not.

$Features{"Virus:SOPHIE"} is the full path to Sophie if it is installed; 0 if it is not.

$Features{"Virus:CLAMD"} is the full path to clamd if it is installed; 0 if it is not.

$Features{"Virus:TROPHIE"} is the full path to Trophie if it is installed; 0 if it is not.

NOTE: Perl-module based features (SpamAssassin, HTMLCleaner and Virus:FileScan) are determined at runtime and may change as these are added and removed. Most Virus features are predetermined at the time of configuration and do not adapt to runtime availability unless changed by the filter rules.

$CWD
This variable holds the working directory for the current message. During filter processing, mimedefang.pl chdir's into this directory before calling any of the filter_ functions. Note that this variable is set correctly in filter_sender and filter_recipient, but not in filter_relay.
$SuspiciousCharsInHeaders
If this variable is true, then mimedefang has discovered suspicious characters in message headers. This might be an exploit for bugs in MIME-parsing routines in some badly-written mail user agents (e.g. Microsoft Outlook.) You should always drop such messages.
$SuspiciousCharsInBody
If this variable is true, then mimedefang has discovered suspicious characters in the message body. This might be an exploit for bugs in MIME-parsing routines in some badly-written mail user agents (e.g. Microsoft Outlook.) You should always drop such messages.
$RelayHostname
The host name of the relay. This is the name of the host which is attempting to send e-mail to your host. May be "undef" if the host name could not be determined. This variable is available in filter_relay, filter_sender and filter_recipient.
$RelayAddr
The IP address of the sending relay (as a string consisting of four dot-separated decimal numbers.) One potential use of $RelayAddr is to limit mailing to certain lists to people within your organization. This variable is available in filter_relay, filter_sender and filter_recipient.
$Helo
The argument given to the SMTP "HELO" command. This variable is available in filter_sender and filter_recipient, but not in filter_relay.
$Subject
The contents of the "Subject:" header.
$Sender
The sender of the e-mail. This variable is set in filter_sender and filter_recipient.
@Recipients
A list of the recipients. In filter_recipient, it is set to the single recipient currently under consideration. Or, after calling read_commands_file within filter_recipient, the current recipient under consideration is in the final position of the array, at $Recipients[-1], while any previous (and accepted) recipients are at the beginning of the array, that is, in @Recipients[0 .. $#Recipients-1].
$MessageID
The contents of the "Message-ID:" header if one is present. Otherwise, contains the string "NOQUEUE".
$QueueID
The Sendmail queue identifier if it could be determined. Otherwise, contains the string "NOQUEUE". This variable is set correctly in filter_sender and filter_recipient, but it is not available in filter_relay.
$MsgID
Set to $QueueID if the queue ID could be determined; otherwise, set to $MessageID. This identifier should be used in logging, because it matches the identifier used by Sendmail to log messages. Note that this variable is set correctly in filter_sender and filter_recipient, but it is not available in filter_relay.
$VirusScannerMessages
Each time a virus-scanning function is called, messages (if any) from the virus scanner are accumulated in this variable. You can use it in filter_end to formulate a notification (if you wish.)
$VirusName
If a virus-scanning function found a virus, this variable will hold the virus name (if it could be determined.)
$SASpamTester
If defined, this is the configured Mail::SpamAssassin object used for mail tests. It may be initialized with a call to spam_assassin_init which also returns it.
%SendmailMacros
This hash contains the values of some Sendmail macros. The hash elements exist only for macros defined by Sendmail. See the Sendmail documentation for the meanings of the macros.

By default, mimedefang passes the values of the following macros: ${daemon_name}, ${if_name}, ${if_addr}, $j, $_, $i, ${tls_version}, ${cipher}, ${cipher_bits}, ${cert_subject}, ${cert_issuer}, ${auth_type}, ${auth_authen}, ${auth_ssf}, ${auth_author}, ${mail_mailer}, ${mail_host} and ${mail_addr}.

If any macro is not set or not passed to milter, it will be unavailable. To access the value of a macro, use: 

	$SendmailMacros{"macro_name"}

Do not place curly brackets around the macro name.
This variable is available in filter_sender and
filter_recipient after a call to read_commands_file.

@SenderESMTPArgs

This array contains all the ESMTP arguments supplied in the MAIL FROM:
command.  For example:

sub print_sender_esmtp_args {
    foreach (@SenderESMTPArgs) {
        print STDERR "Sender ESMTP arg: $_n";
    }
}

%RecipientESMTPArgs

This hash contains all the ESMTP arguments supplied in each RCPT TO:
command.  For example:

sub print_recip_esmtp_args {
    foreach my $recip (@Recipients) {
        foreach(@{$RecipientESMTPArgs{$recip}}) {
            print STDERR "Recip ESMTP arg for $recip: $_n";
        }
    }
}

%RecipientMailers

This hash contains the Sendmail "mailer-host-address" triple for each
recipient.  Here's an example of how to use it:

sub print_mailer_info {
    my($recip, $mailer, $host, $addr);
    foreach $recip (@Recipients) {
        $mailer = ${RecipientMailers{$recip}}[0];
        $host = ${RecipientMailers{$recip}}[1];
        $addr =  ${RecipientMailers{$recip}}[2];
        print STDERR "$recip: mailer=$mailer, host=$host, addr=$addr\n";
    }
}

In filter_recipient, this variable by default only contains
information on the recipient currently under investigation. Information
on all recipients is available after calling read_commands_file.

ACTIONS
When the filter procedure decides how to dispose of a part, it should
call one or more action_ subroutines.  The action subroutines are:

action_accept()

Accept the part.

action_rebuild() 

Rebuild the mail body, even if mimedefang thinks no changes were made.
Normally, mimedefang does not alter a message if no changes were
made.  action_rebuild may be used if you make changes to
entities directly (by manipulating the MIME::Head, for example.)
Unless you call action_rebuild, mimedefang will be unaware
of the changes.  Note that all the built-in action... routines
which change a message implicitly call action_rebuild.

action_add_header($hdr, $val)

Add a header from the message.  This can be used in filter_begin
or filter_end.  The $hdr component is the header name
without the colon, and the $val is the header value.  For example,
to add the header:

	X-MyHeader: A nice piece of text

use:

	action_add_header("X-MyHeader", "A nice piece of text");

action_change_header($hdr, $val, $index)

Changes an existing header in the message. This can be used in
filter_begin or filter_end.  The $hdr parameter is the
header name without the colon, and $val is the header value.
If the header does not exist, then a header with the given name and
value is added.

The $index parameter is optional; it defaults to 1.  If you supply it,
then the $index'th occurrence of the header is changed, if there is
more than one header with the same name.  (This is common with the
Received: header, for example.)

action_delete_header($hdr, $index)

Deletes an existing header in the message. This can be used in
filter_begin or filter_end.  The $hdr parameter is the
header name without the colon.

The $index parameter is optional; it defaults to 1.  If you supply it,
then the $index'th occurrence of the header is deleted, if there is
more than one header with the same name.

action_delete_all_headers($hdr)

Deletes all headers with the specified name.  This can be used in
filter_begin or filter_end.  The $hdr parameter is the
header name without the colon.

action_drop()

Drop the part.  If called from filter_multipart, drops all
contained parts also.

action_drop_with_warning($msg)

Drop the part, but add the warning $msg to the e-mail message.
If called from filter_multipart, drops all contained parts also.

action_accept_with_warning($msg)

Accept the part, but add the warning $msg to the e-mail message.

action_replace_with_warning($msg)

Drop the part and replace it with a text part $msg.
If called from filter_multipart, drops all contained parts also.

action_replace_with_url($entity, $doc_root, $base_url, $msg, [$cd_data, $salt])

Drop the part, but save it in a unique location under $doc_root.
The part is replaced with the text message $msg.  The string "_URL_"
in $msg is replaced with $base_url/something, which can be used
to retrieve the message.

You should not use this function in filter_multipart.

This action is intended for stripping large parts out of the message
and replacing them to a link on a Web server.  Here's how you would
use it in filter():

$size = (stat($entity->bodyhandle->path))[7];
if ($size > 1000000) {
	return action_replace_with_url($entity,
		"/home/httpd/html/mail_parts",
		"http://mailserver.company.com/mail_parts",
		"The attachment was larger than 1,000,000 bytes.\n" .
		"It was removed, but may be accessed at this URL:\n\n" .
		"\t_URL_\n");
}

This example moves attachments greater than 1,000,000 bytes into
/home/httpd/html/mail_parts and replaces them with a link.  The
directory should be accessible via a Web server at
http://mailserver.company.com/mail_parts.

The generated name is created by performing a SHA1 hash of the part and
adding the extension to the ASCII-HEX representation of the hash.  If many
different e-mails are sent containing an identical large part, only one copy
of the part is stored, regardless of the number of senders or recipients.

For privacy reasons, you must turn off Web server indexing in the
directory in which you place mail parts, or anyone will be able to read
them.  If indexing is disabled, an attacker would have to guess the SHA1
hash of a part in order to read it.

Optionally, a fifth argument can supply data to be saved into a hidden
dot filename based on the generated name.  This data can then be read in
on the fly by a CGI script or mod_perl module before serving the file to
a web client, and used to add information to the response, such as
Content-Disposition data.

A sixth optional argument, $salt, is mixed in to the SHA1 hash.  This
salt can be any string and should be kept confidential.  The salt is
designed to prevent people from guessing whether or not a particular
attachment has been received on your server by altering the SHA1 hash
calculation.

action_defang($entity, $name, $fname, $type)

Accept the part, but change its name to $name, its suggested filename
to $fname and its MIME type to $type.  If $name or
$fname are "", then mimedefang.pl generates generic names.
Do not use this action in filter_multipart.

If you use action_defang, you must define a subroutine called
defang_warning in your filter.  This routine takes two arguments:
$oldfname (the original name of an attachment) and $fname (the defanged
version.)  It should return a message telling the user what happened.  For
example:

sub defang_warning {
    my($oldfname, $fname) = @_;
    return "The attachment '$oldfname' was renamed to '$fname'\n";
}

action_external_filter($entity, $cmd)

Run an external UNIX command $cmd.  This command must read the part
from the file ./FILTERINPUT and leave the result in ./FILTEROUTPUT.
If the command executes successfully, returns 1, otherwise 0.  You can
test the return value and call another action_ if the filter failed.
Do not use this action in filter_multipart.

action_quarantine($entity, $msg)

Drop and quarantine the part, but add the warning $msg to the
e-mail message.

action_quarantine_entire_message($msg)

Quarantines the entire message in a quarantine directory on the mail server,
but does not otherwise affect disposition of the message.
If "$msg" is non-empty, it is included in any administrator notification.

action_sm_quarantine($reason)

Quarantines a message in the Sendmail mail queue using the new
QUARANTINE facility of Sendmail 8.13.  Consult the Sendmail documentation
for details about this facility.  If you use action_sm_quarantine
with a version of Sendmail that lacks the QUARANTINE facility,
mimedefang will log an error message and not quarantine the message.

action_bounce($reply, $code, $dsn)

Reject the entire e-mail message with an SMTP failure code, and the
one-line error message $reply.  If the optional $code and $dsn
arguments are supplied, they specify the numerical SMTP reply code and
the extended status code (DSN code).  If the codes you supply do not
make sense for a bounce, they are replaced with "554" and "5.7.1"
respectively.

action_bounce merely makes a note that the message is to
be bounced; remaining parts are still processed.  If
action_bounce is called for more than one part, the mail is
bounced with the message in the final call to action_bounce.
You can profitably call action_quarantine followed by
action_bounce if you want to keep a copy of the offending part.
Note that the message is not bounced immediately; rather, remaining
parts are processed and the message is bounced after all parts have
been processed.

Note that despite its name, action_bounce does not generate
a "bounce message".  It merely rejects the message with an SMTP
failure code.

WARNING:
action_bounce() may cause the sending relay to generate spurious
bounce messages if the sender address is faked.  This is a particular
problem with viruses.  However, we believe that on balance, it's
better to bounce a virus than to silently discard it.  It's almost
never a good idea to hide a problem.

action_tempfail($msg, $code, $dsn)

Cause an SMTP "temporary failure" code to be returned, so the sending
mail relay requeues the message and tries again later.  The message
$msg is included with the temporary failure code.  If the optional
$code and $dsn arguments are supplied, they specify the numerical SMTP
reply code and the extended status code (DSN code).  If the codes you
supply do not make sense for a temporary failure, they are replaced
with "450" and "4.7.1" respectively.

action_discard()

Silently discard the message, notifying nobody.  You can profitably
call action_quarantine followed by action_discard if you
want to keep a copy of the offending part.  Note that the message is
not discarded immediately; rather, remaining parts are processed and
the message is discarded after all parts have been processed.

action_notify_sender($message)

This action sends an e-mail back to the original sender with the indicated
message.  You may call another action after this one.  If
action_notify_sender is called more than once, the messages are
accumulated into a single e-mail message -- at most one notification message
is sent per incoming message.  The message should be terminated with a newline.

The notification is delivered in deferred mode; you should run a client-queue
runner if you are using Sendmail 8.12.

NOTE: Viruses often fake the sender address.  For that reason,
if a virus-scanner has detected a virus, action_notify_sender is
disabled and will simply log an error message if you try to use it.

action_notify_administrator($message)

This action e-mails the MIMEDefang administrator the supplied message.
You may call another action after this one;
action_notify_administrator does not affect mail processing.  If
action_notify_administrator is called more than once, the messages are
accumulated into a single e-mail message -- at most one notification
message is sent per incoming message.  The message should be
terminated with a newline.

The notification is delivered in deferred mode; you should run a client-queue
runner if you are using Sendmail 8.12.

anomy_clean_html($entity, {" name" => val , ...})

If you have the Anomy mail cleaning tools (http://mailtools.anomy.net) and
have installed the Anomy modules in a standard Perl include directory,
this function uses an Anomy::HTMLCleaner object to sanitize the HTML
code in $entity, which assumed to be of type text/html.  The configuration
arguments are optional; possible values are documented in comments
in the Anomy/HTMLCleaner.pm Perl module.

append_text_boilerplate($entity, $boilerplate, $all)

This action should only be called from filter_end.  It appends
the text "\n$boilerplate\n" to the first text/plain part (if $all is 0)
or to all text/plain parts (if $all is 1).

append_html_boilerplate($entity, $boilerplate, $all)

This action should only be called from filter_end.  It adds
the text "\n$boilerplate\n" to the first text/html part (if $all is 0)
or to all text/html parts (if $all is 1).  This function tries
to be smart about inserting the boilerplate; it uses HTML::Parser to
detect closing tags and inserts the boilerplate before the </body> tag
if there is one, or before the </html> tag if there is no </body>.  If
there is no </body> or </html> tag, it appends the boilerplate to the end of
the part.

Do not use append_html_boilerplate unless you have installed the
HTML::Parser Perl module.

Here is an example illustrating how to use the boilerplate functions:

	sub filter_end {
		my($entity) = @_;
		append_text_boilerplate($entity,
			"Lame text disclaimer", 0);
		append_html_boilerplate($entity,
			"<em>Lame</em> HTML disclaimer", 0);
	}

action_add_part($entity, $type, $encoding, $data, $fname, $disposition [, $offset])

This action should only be called from the filter_end
routine.  It adds a new part to the message, converting the original
message to mutipart if necessary.  The function returns the part so
that additional mime attributes may be set on it.  Here's an example:

	sub filter_end {
		my($entity) = @_;

		action_add_part($entity, "text/plain", "-suggest",
 				"This e-mail does not represent" .
				"the official policy of FuBar, Inc.\n",
				"disclaimer.txt", "inline");
        }


The $entity parameter must be the argument passed in to
filter_end.  The $offset parameter is optional; if omitted, it
defaults to -1, which adds the new part at the end.  See the
MIME::Entity man page and the add_part member function for the
meaning of $offset.

Note that action_add_part tries to be more intelligent than simply
calling $entity->add_part.  The decision process is as follows:

o

If the top-level entity is multipart/mixed, then the part is simply added.

o

Otherwise, a new top-level multipart/mixed container is generated, and
the original top-level entity is made the first part of the multipart/mixed
container.  The new part is then added to the multipart/mixed container.

USEFUL ROUTINES
mimedefang.pl includes some useful functions you can call from
your filter:

detect_and_load_perl_modules()

Unless you really know what you're doing, this function
must be called first thing in your filter file.  It causes
mimedefang.pl to detect and load Perl modules such
as Mail::SpamAssassin, Net::DNS, etc., and to populate the
%Features hash.

send_quarantine_notifications()

This function should be called from filter_end.  If any parts were
quarantined, a quarantine notification is sent to the MIMEDefang
administrator.  Please note that if you do not call
send_quarantine_notifications, then no quarantine notifications
are sent.

get_quarantine_dir()

This function returns the full path name of the quarantine directory.
If you have not yet quarantined any parts of the message, a quarantine
directory is created and its pathname returned.

add_recipient($recip)

This function adds $recip to the list of envelope recipients.  A copy
of the message (after any modifications by MIMEDefang) will be sent to
$recip in addition to the original recipients.  Note that add_recipient
does not modify the @Recipients array; it just makes a note to Sendmail
to add the recipient.

delete_recipient($recip)

This function deletes $recip from the list of recipients.  That person
will not receive a copy of the mail.  $recip should exactly match an
entry in the @Recipients array for delete_recipient() to work.  Note
that delete_recipient does not modify the @Recipients array;
it just makes a note to Sendmail to delete the recipient.

resend_message($recip1, $recip2, ...)

or

resend_message(@recips)

This function immediately resends the original, unmodified
mail message to each of the named recipients.  The sender's address is
preserved.  Be very careful when using this function, because it resends
the original message, which may contain undesired attachments.  Also,
you should not call this function from filter(), because it resends
the message each time it is called.  This may result in multiple
copies being sent if you are not careful.  Call from filter_begin() or
filter_end() to be safe.

The function returns true on success, or false if it fails.

Note that the resend_message function delivers the mail in deferred
mode (using Sendmail's "-odd" flag.)  You must run a client-submission
queue processor if you use Sendmail 8.12.  We recommend executing this
command as part of the Sendmail startup sequence:

	sendmail -Ac -q5m

remove_redundant_html_parts($entity)

This function should only be called from filter_end.
It removes redundant HTML parts from the message.  It works by deleting
any part of type text/html from the message if (1) it is a sub-part of
a multipart/alternative part, and (2) there is another part of type
text/plain under the multipart/alternative part.

replace_entire_message($entity)

This function can only be called from filter_end.  It replaces
the entire message with $entity, a MIME::Entity object that you have
constructed.  You can use any of the MIME::Tools functions to construct
the entity.

read_commands_file()

This function should only be called from filter_sender and
filter_recipient. This will read the COMMANDS file (as
described in mimedefang-protocol(7)), and will fill or update the
following global variables: $Sender, @Recipients, %RecipientMailers,
$RelayAddr, $RealRelayAddr, $RelayHostname, $RealRelayHostname,
$QueueID, $Helo, %SendmailMacros.

If you do not call read_commands_file, then the only information
available in filter_sender and filter_recipient is that
which is passed as an argument to the function.

stream_by_domain()

Do not use this function unless you have Sendmail 8.12 and locally-
submitted e-mail is submitted using SMTP.

This function should only be called at the very beginning of
filter_begin(), like this:

	sub filter_begin {
		if (stream_by_domain()) {
			return;
		}
		# Rest of filter_begin
	}

stream_by_domain() looks at all the recipients of the message, and if
they belong to the same domain (e.g., joe@domain.com, jane@domain.com and
sue@domain.com), it returns 0 and sets the global variable $Domain to
the domain (domain.com in this example.)

If users are in different domains, stream_by_domain() resends
the message (once to each domain) and returns 1 For example, if the
original recipients are joe@abc.net, jane@xyz.net and sue@abc.net, the
original message is resent twice: One copy to joe@abc.net and
sue@abc.net, and another copy to jane@xyz.net.  Also, any subsequent
scanning is canceled (filter() and filter_end() will not be
called for the original message) and the message is silently
discarded.

If you have Sendmail 8.12, then locally-submitted messages are sent via
SMTP, and MIMEDefang will be called for each resent message.
It is possible to set up Sendmail 8.12 so locally-submitted messages
are delivered directly; in this case, stream_by_domain will not
work.

Using stream_by_domain allows you to customize your filter rules for
each domain.  If you use the function as described above, you can do
this in your filter routine:

	sub filter {
		my($entity, $fname, $ext, $type) = @_;
		if ($Domain eq "abc.com") {
			# Filter actions for abc.com
		} elsif ($Domain eq "xyz.com") {
			# Filter actions for xyz.com
		} else {
			# Default filter actions
		}
	}

You cannot rely on $Domain being set unless you have called
stream_by_domain().

stream_by_recipient()

Do not use this function unless you have Sendmail 8.12 and locally-
submitted e-mail is submitted using SMTP.

This function should only be called at the very beginning of
filter_begin(), like this:

	sub filter_begin {
		if (stream_by_recipient()) {
			return;
		}
		# Rest of filter_begin
	}

If there is more than one recipient, stream_by_recipient() resends the
message once to each recipient.  That way, you can customize your
filter rules on a per-recipient basis.  This may increase the load on
your mail server considerably.

Also, a "recipient" is determined before alias expansion.  So
"all@mydomain.com" is considered a single recipient, even if Sendmail
delivers to a list.

If you have Sendmail 8.12, then locally-submitted messages are sent via
SMTP, and MIMEDefang will be called for each resent message.
It is possible to set up Sendmail 8.12 so locally-submitted messages
are delivered directly; in this case, stream_by_recipient() will not
work.

stream_by_recipient() allows you to customize your filter rules for
each recipient in a manner similar to stream_by_domain().

LOGGING
md_graphdefang_log_enable($facility, $enum_recips)

Enables the md_graphdefang_log function (described next).  The function logs to syslog
using the specified facility.  If you omit $facility, it defaults to 'mail'.
If you do not call md_graphdefang_log_enable in your filter, then any calls to md_graphdefang_log
simply do nothing.

If you supply $enum_recips as 1, then a line of logging is output for
each recipient of a mail message.  If it is zero, then only a
single line is output for each message.  If you omit $enum_recips,
it defaults to 1.

md_graphdefang_log($event, $v1, $v2)

Logs an event with up to two optional additional parameters.  The log
message has a specific format useful for graphing tools; the
message looks like this:

	MDLOG,msgid,event,v1,v2,sender,recipient,subj

"MDLOG" is literal text.  "msgid" is the Sendmail queue identifier.
"event" is the event name, and "v1" and "v2" are the additional
parameters.  "sender" is the sender's e-mail address. "recipient"
is the recipient's e-mail address, and "subj" is the message subject.
If a message has more than one recipient, md_graphdefang_log may log an event message
for each recipient, depending on how you called md_graphdefang_log_enable.

Note that md_graphdefang_log should not be used in filter_relay, filter_sender
or filter_recipient.  The global variables it relies on are not
valid in that context.

If you want to log general text strings, do not use md_graphdefang_log.
Instead, use md_syslog (described next).

md_syslog($level, $msg)

Logs the message $msg to syslog, using level $level.  The level
is a literal string, and should be one of 'err', 'debug', 'warning',
'emerg', 'crit', 'notice' or 'info'.  (See syslog(3) for details.)

Note that md_syslog does not perform %-subsitutions like
syslog(3) does.  Depending on your Perl installation, md_syslog boils
down to a call to Unix::Syslog::syslog or Sys::Syslog::syslog.  See the
Unix::Syslog or Sys::Syslog man pages for more details.

md_openlog($tag, $facility)

Sets the tag used in syslog messages to $tag, and sends the logs to the
$facility facility.  If you do not call md_openlog before you call
md_syslog, then it is called implicitly with $tag set to mimedefang.pl
and $facility set to mail.

RBL LOOKUP FUNCTIONS
mimedefang.pl includes the following functions for lookup up
IP addresses in DNS-based real-time blacklists.

relay_is_blacklisted($relay, $domain)

This checks a DNS-based real-time spam blacklist, and returns true if
the relay host is blacklisted, or false otherwise.  (In fact, the
return value is whatever the blacklist returns as a resolved
hostname, such as "127.0.0.4")

Note that relay_is_blacklisted uses the built-in
gethostbyname function; this is usually quite inefficient
and does not permit you to set a timeout on the lookup.  Instead,
we recommend using one of the other DNS lookup function described in
this section.  (Note, though, that the other functions require the Perl
Net::DNS module, whereas relay_is_blacklisted does not.)

Here's an example of how to use relay_is_blacklisted:

	if (relay_is_blacklisted($RelayAddr, "rbl.spamhaus.org")) {
		action_add_header("X-Blacklist-Warning",
			  "Relay $RelayAddr is blacklisted by Spamhaus");
	}

relay_is_blacklisted_multi($relay, $timeout, $answers_wanted, [$domain1, $domain2, ...], $res)

This function is similar to relay_is_blacklisted, except that it takes
a timeout argument (specified in seconds) and an array of domains to check.
The function checks all domains in parallel, and is guaranteed to return
in $timeout seconds.  (Actually, it may take up to one second longer.)

The parameters are:

$relay -- the IP address you want to look up

$timeout -- a timeout in seconds after which the function should return

$answers_wanted -- the maximum number of positive answers you care about.
For example, if you're looking up an address in 10 different RBLs, but
are going to bounce it if it is on four or more, you can set $answers_wanted
to 4, and the function returns as soon as four "hits" are discovered.  If
you set $answers_wanted to zero, then the function does not return early.

[$domain1, $domain2, ...] -- a reference to an array of strings, where
each string is an RBL domain.

$res -- a Net::DNS::Resolver object.  This argument is optional; if you
do not supply it, then relay_is_blacklisted_multi constructs its
own resolver.

The return value is a reference to a hash; the keys of the hash are
the original domains, and the corresponding values are either SERVFAIL,
NXDOMAIN, or a list of IP addresses in dotted-quad notation.

Here's an example:

    $ans = relay_is_blacklisted_multi($RelayAddr, 8, 0,
        ["sbl.spamhaus.org", "relays.ordb.org"]);

    foreach $domain (keys(%$ans)) {
        $r = $ans->{$domain};
        if (ref($r) eq "ARRAY") {
            # It's an array -- it IS listed in RBL
            print STDERR "Lookup in $domain yields [ ";
            foreach $addr (@$r) {
                print STDERR $addr . " ";
            }
            print STDERR "]\n";
        } else {
            # It is NOT listed in RBL
            print STDERR "Lookup in $domain yields "
                         . $ans->{$domain} . "\n";
        }
    }


You should compare each of $ans->{$domain} to "SERVFAIL" and "NXDOMAIN"
to see if the relay is not listed.  Any other return value will
be an array of IP addresses indicating that the relay is listed.

Any lookup that does not succeed within $timeout seconds has the
corresponding return value set to SERVFAIL.

relay_is_blacklisted_multi_list($relay, $timeout, $answers_wanted, [$domain1, $domain2, ...], $res)

This function is similar to relay_is_blacklisted_multi except that
the return value is simply an array of RBL domains in which the relay
was listed.

relay_is_blacklisted_multi_count($relay, $timeout, $answers_wanted, [$domain1, $domain2, ...], $res)

This function is similar to relay_is_blacklisted_multi except that
the return value is an integer specifying the number of domains on which
the relay was blacklisted.

TEST FUNCTIONS
mimedefang.pl includes some "test" functions:

md_version()

returns the version of MIMEDefang as a string (for example, "2.53").

message_rejected()

Returns true if any of action_tempfail, action_bounce or
action_discard have been called for this message; returns false
otherwise.


If you have the Mail::SpamAssassin Perl module installed (see
http://www.spamassassin.org) you may call any of the spam_assassin_*
functions.  They should only be called from filter_begin or
filter_end because they operate on the entire message at once.
Most functions use an optionally provided config file.  If no config
file is provided, mimedefang.pl will look for one of three default
SpamAssassin preference files.  The first of the following found will
be used:

o

/etc/sa-mimedefang.cf
o
/etc/mail/sa-mimedefang.cf

o

/etc/spamassassin/local.cf

o

/etc/spamassassin.cf


Important Note:  MIMEDefang does not permit SpamAssassin
to modify messages.  If you want to tag spam messages with special headers
or alter the subject line, you must use MIMEDefang functions to do it.
Setting SpamAssassin configuration options to alter messages will not work.

spam_assassin_is_spam([ $config_file ])

Determine if the current message is SPAM/UCE as determined by SpamAssassin.
Compares the score of the message against the threshold score (see below)
and returns true if it is.  Uses spam_assassin_check below.

spam_assassin_check([ $config_file ])

This function returns a four-element list of the form ($hits, $required, 
$tests, $report).  $hits is the "score" given to the message by SpamAssassin
(higher score means more likely SPAM). $required is the number of hits 
required before SpamAssassin concludes that the message is SPAM.  $tests
is a comma-separated list of SpamAssassin test names, and $report is text
detailing which tests triggered and their point score.  This gives you 
insight into why SpamAssassin concluded that the message is SPAM.  Uses 
spam_assassin_status below.
  

spam_assassin_status([ $config_file ])

This function returns a Mail::SpamAssasin::PerMsgStatus object.  Read the 
SpamAssassin documentation for details about this object.  You are 
responsible for calling the finish method when you are done with it.
Uses spam_assassin_init and spam_assassin_mail below.

spam_assassin_init([ $config_file ])

This function returns the new global Mail::SpamAssassin object with the 
specified or default config (outlined above).  If the global object is
already defined, returns it -- does not change config files!  The object
can be used to perform other SpamAssassin related functions.

spam_assassin_mail()

This function returns a Mail::SpamAssassin::NoMailAudit object with the 
current email message contained in it.  It may be used to perform other 
SpamAssassin related functions.

md_copy_orig_msg_to_work_dir()

Normally, virus-scanners are passed only the unpacked, decoded parts
of a MIME message.  If you want to pass the original, undecoded message
in as well, call md_copy_orig_msg_to_work_dir prior to
calling message_contains_virus.

md_copy_orig_msg_to_work_dir_as_mbox_file()

Normally, virus-scanners are passed only the unpacked, decoded parts
of a MIME message.  If you want to pass the original, undecoded
message in as a UNIX-style "mbox" file, call
md_copy_orig_msg_to_work_dir_as_mbox_file prior to calling
message_contains_virus.  The only difference between this function
and md_copy_orig_msg_to_work_dir is that this function prepends
a "From_" line to make the message look like a UNIX-style mbox file.
This is required for some virus scanners (such as Clam AntiVirus) to
recognize the file as an e-mail message.

message_contains_virus()

This function runs every installed virus-scanner and returns
the scanner results.  The function should be called in list context;
the return value is a three-element list ($code, $category, $action).

$code is the actual return code from the virus scanner.

$category is a string categorizing the return code:

"ok" - no viruses detected.

"not-installed" - indicated virus scanner is not installed.

"cannot-execute" - for some reason, the scanner could not be executed.

"virus" - a virus was found.

"suspicious" - a "suspicious" file was found.

"interrupted" - scanning was interrupted.

"swerr" - an internal scanner software error occurred.

$action is a string containing the recommended action:

"ok" - allow the message through unmolested.

"quarantine" - a virus was detected; quarantine it.

"tempfail" - something went wrong; tempfail the message.

message_contains_virus_trend()

message_contains_virus_nai()

message_contains_virus_bdc()

message_contains_virus_nvcc()

message_contains_virus_csav()

message_contains_virus_fsav()

message_contains_virus_hbedv()

message_contains_virus_vexira()

message_contains_virus_sophos()

message_contains_virus_clamav()

message_contains_virus_avp()

message_contains_virus_avp5()

message_contains_virus_filescan()

message_contains_virus_fprot()

message_contains_virus_fprotd()

These functions should be called in list context.  They use the
indicated anti-virus software to scan the message for viruses.  These
functions are intended for use in filter_begin() to make an initial
scan of the e-mail message.

The supported virus scanners are:

nai

NAI "uvscan" - http://www.nai.com/

Bitdefender "bdc" - http://www.bitdefender.com/

csav

Command Anti-Virus - http://www.commandsoftware.com/

fsav

F-Secure Anti-Virus - http://www.f-secure.com/

hbedv

H+BEDV "AntiVir" - http://www.hbedv.com/

vexira

Vexira "Vexira" - http://www.centralcommand.com/

sophos

Sophos AntiVirus - http://www.sophos.com/

avp

Kaspersky AVP and aveclient (AVP5) - http://www.avp.ru/

clamav

Clam AntiVirus - http://www.clamav.net/

f-prot

F-RISK F-PROT - http://www.f-prot.com/

message_contains_virus_openantivirus([$host])

Connects to the specified host:port (default $OpenAVHost), where
the OpenAntiVirus daemon is expected to be listening.  Return values
are the same as the other message_contains_virus functions.

message_contains_virus_carrier_scan([$host])

Connects to the specified host:port:local_or_nonlocal (default
$CSSHost), where the Symantec CarrierScan Server daemon is
expected to be listening.  Return values are the same as the other
message_contains_virus functions.

message_contains_virus_sophie([$sophie_sock])

Connects to the specified socket (default $SophieSock), where
the Sophie daemon is expected to be listening.  Return values are the
same as the other message_contains_virus functions.

message_contains_virus_clamd([$clamd_sock])

Connects to the specified socket (default $ClamdSock), where
the clamd daemon is expected to be listening.  Return values are the
same as the other message_contains_virus functions.

message_contains_virus_trophie([$trophie_sock])

Connects to the specified socket (default $TrophieSock), where
the Trophie daemon is expected to be listening.  Return values are the
same as the other message_contains_virus functions.

entity_contains_virus($entity)

This function runs the specified MIME::Entity through
every installed virus-scanner and returns
the scanner results.  The return values are the same as
for message_contains_virus().

entity_contains_virus_trend($entity)

entity_contains_virus_nai($entity)

entity_contains_virus_bdc($entity)

entity_contains_virus_nvcc($entity)

entity_contains_virus_csav($entity)

entity_contains_virus_fsav($entity)

entity_contains_virus_hbedv($entity)

entity_contains_virus_sophos($entity)

entity_contains_virus_clamav($entity)

entity_contains_virus_avp($entity)

entity_contains_virus_avp5($entity)

entity_contains_virus_filescan($entity)

entity_contains_virus_fprot($entity)

entity_contains_virus_fprotd($entity)

These functions, meant to be called from filter(), are similar to the
message_contains_virus functions except they scan only the current part.
They should be called from list context, and their return values are as
described for the message_contains_virus functions.

entity_contains_virus_openantivirus($entity[, $host])

Connects to the specified host:port (default $OpenAVHost), where
the OpenAntiVirus daemon is expected to be listening.  Return values
are the same as the other entity_contains_virus functions.

entity_contains_virus_carrier_scan($entity[, $host])

Connects to the specified host:port:local_or_nonlocal (default
$CSSHost), where the Symantec CarrierScan Server daemon is
expected to be listening.  Return values are the same as the other
entity_contains_virus functions.

entity_contains_virus_sophie($entity[, $sophie_sock])

Connects to the specified socket (default $SophieSock), where
the Sophie daemon is expected to be listening.  Return values
are the same as the other entity_contains_virus functions.

entity_contains_virus_trophie($entity[, $trophie_sock])

Connects to the specified socket (default $TrophieSock), where
the Trophie daemon is expected to be listening.  Return values
are the same as the other entity_contains_virus functions.

entity_contains_virus_clamd($entity[, $clamd_sock])

Connects to the specified socket (default $ClamdSock), where
the clamd daemon is expected to be listening.  Return values
are the same as the other entity_contains_virus functions.

SMTP FLOW
This section illustrates the flow of messages through MIMEDefang.

1. INITIAL CONNECTION

If you invoked mimedefang with the -r option and have
defined a filter_relay routine, it is called.

2. SMTP HELO COMMAND

The HELO string is stored internally, but no filter functions are called.

3. SMTP MAIL FROM: COMMAND

If you invoked mimedefang with the -s option and have
defined a filter_sender routine, it is called.

4. SMTP RCPT TO: COMMAND

If you invoked mimedefang with the -t option and have
defined a filter_recipient routine, it is called.

5. END OF SMTP DATA

filter_begin is called.  For each MIME part, filter is called.  Then
filter_end is called.

PRESERVING RELAY INFORMATION

Most organizations have more than one machine handling internet
e-mail.  If the primary machine is down, mail is routed to a secondary
(or tertiary, etc.) MX server, which stores the mail until the primary
MX host comes back up.  Mail is then relayed to the primary MX host.


Relaying from a secondary to a primary MX host has the unfortunate
side effect of losing the original relay's IP address information.
MIMEDefang allows you to preserve this information.  One way around
the problem is to run MIMEDefang on all the secondary MX hosts
and use the same filter.  However, you may not have control over the
secondary MX hosts.  If you can persuade the owners of the secondary MX
hosts to run MIMEDefang with a simple filter which only preserves relay
information and does no other scanning, your primary MX host can
obtain relay information and make decisions using $RelayAddr and
$RelayHostname.


When you configure MIMEDefang, supply the "--with-ipheader" argument
to the ./configure script.  When you install MIMEDefang, a file
called /etc/mimedefang-ip-key will be created, which
contains a randomly-generated header name.  Copy this file to all
of your mail relays.  It is important that all of your MX hosts
have the same key.  The key should be kept confidential, but it's
not disastrous if it leaks out.


On your secondary MX hosts, add this line to filter_end:

	add_ip_validation_header();


Note:  You should only add the validation header to mail
destined for one of your other MX hosts!  Otherwise, the validation
header will leak out.


When the secondary MX hosts relay to the primary MX host, $RelayAddr
and $RelayHostname will be set based on the IP validation header.  If
MIMEDefang notices this header, it sets the global variable $WasResent
to 1.  Since you don't want to trust the header unless it was set by
one of your secondary MX hosts, you should put this code in
filter_begin:

	if ($WasResent) {
		if ($RealRelayAddr ne "ip.of.secondary.mx" and
		    $RealRelayAddr ne "ip.of.tertiary.mx") {
			$RelayAddr = $RealRelayAddr;
			$RelayHostname = $RealRelayHostname;
		}
	}

This resets the relay address and hostname to the actual relay address and
hostname, unless the message is coming from one of your other MX hosts.


On the primary MX host, you should add this in filter_begin:

	delete_ip_validation_header();


This prevents the validation header from leaking out to recipients.


Note: The IP validation header works only in message-oriented
functions.  It (obviously) has no effect on filter_relay,
filter_sender and filter_recipient, because no header
information is available yet.  You must take this into account when
writing your filter; you must defer relay-based decisions to
the message filter for mail arriving from your other MX hosts.

GLOBAL VARIABLE LIFETIME
The following list describes the lifetime of global variables (thanks to Tony
Nugent for providing this documentation.)

If you set a global variable:

Outside a subroutine in your filter file

It is available to all functions, all the time.

In filter_relay, filter_sender or filter_recipient

Not guaranteed to be available to any other function, not even
from one filter_recipient call to the next, when receiving a
multi-recipient email message.

In filter_begin

Available to filter_begin, filter and filter_end

In filter

Available to filter and filter_end

In filter_end

Available within filter_end


The "built-in" globals like $Subject, $Sender, etc. are always available
to filter_begin, filter and filter_end. Some are available to filter_relay,
filter_sender or filter_recipient, but you should check the documentation
of the variable above for details.

MAINTAINING STATE

There are four basic groups of filtering functions:

1

filter_relay

2

filter_sender

3

filter_recipient

4

filter_begin, filter, filter_multipart, filter_end


In general, for a given mail message, these groups of functions may
be called in completely different Perl processes.  Thus, there is
no way to maintain state inside Perl between groups of functions.
That is, you cannot set a variable in filter_relay and expect it
to be available in filter_sender, because the filter_sender
invocation might take place in a completely different process.


However, for a given mail message, the $CWD global variable holds
the message spool directory, and the current working directory is set to
$CWD.  Therefore, you can store state in files inside $CWD.  If
filter_sender stores data in a file inside $CWD, then
filter_recipient can retrieve that data.


Since filter_relay is called directly after a mail connection is
established, there is no message context yet, no per-message mimedefang
spool directory, and the $CWD global is not set. Therefore, it is not
possible to share information from filter_relay to one of the
other filter functions. The only thing that filter_relay has in
common with the other functions are the values in the globals $RelayAddr
and $RelayHostname. These could be used to access per-remote-host
information in some database.


Inside $CWD, we reserve filenames beginning with upper-case letters for
internal MIMEDefang use.  If you want to create files to store state,
name them beginning with a lower-case letter to avoid clashes with
future releases of MIMEDefang.

SOCKET MAPS
If you have Sendmail 8.13 or later, and have compiled it with the
SOCKETMAP option, then you can use a special map type that communicates
over a socket with another program (rather than looking up a key
in a Berkeley database, for example.)


mimedefang-multiplexor implements the Sendmail SOCKETMAP protocol
if you supply the -N option.  In that case, you can define a function
called filter_map to implement map lookups.  filter_map
takes two arguments:  $mapname is the name of the Sendmail map (as given
in the K sendmail configuration directive), and $key is the key to be looked
up.


filter_map must return a two-element list: ($code, $val)
$code can be one of:

OK

The lookup was successful.  In this case, $val must be the result of the
lookup

NOTFOUND

The lookup was unsuccessful -- the key was not found.  In this case, $val
should be the empty string.

TEMP

There was a temporary failure of some kind.  $val can be an explanatory
error message.

TIMEOUT

There was a timeout of some kind.  $val can be an explanatory
error message.

PERM

There was a permanent failure.  This is not the same as an
unsuccessful lookup; it should be used only to indicate a serious
misconfiguration.  As before, $val can be an explanatory error message.


Consider this small example.  Here is a minimal Sendmail configuration
file:

	V10/Berkeley
	Kmysock socket unix:/var/spool/MIMEDefang/map.sock
	kothersock socket unix:/var/spool/MIMEDefang/map.sock


If mimedefang-multiplexor is invoked with the arguments
-N unix:/var/spool/MIMEDefang/map.sock, and the filter
defines filter_map as follows:

	sub filter_map ($$) {
	    my($mapname, $key) = @_;
	    my $ans;
	    if($mapname ne "mysock") {
	        return("PERM", "Unknown map $mapname");
	    }
	    $ans = reverse($key);
	    return ("OK", $ans);
	}

Then in Sendmail's testing mode, we see the following:

	> /map mysock testing123
	map_lookup: mysock (testing123) returns 321gnitset (0)
	> /map othersock foo
	map_lookup: othersock (foo) no match (69)


(The return code of 69 means EX_UNAVAILABLE or Service Unavailable)


A real-world example could do map lookups in an LDAP directory or SQL
database, or perform other kinds of processing.  You can even implement
standard Sendmail maps like virtusertable, mailertable, access_db, etc.
using SOCKETMAP.

TICK REQUESTS


If you supply the -X option to mimedefang-multiplexor,
then every so often, a "tick" request is sent to a free slave.  If
your filter defines a function called filter_tick, then this
function is called with a single argument: the tick type.  If you
run multiple parallel ticks, then each tick has a type ranging from 0
to n-1, where n is the number of parallel ticks.  If you're
only running one tick request, then the argument to filter_tick
is always 0.

You can use this facility to run periodic tasks from within
MIMEDefang.  Note, however, that you have no control over which slave
is picked to run filter_tick.  Also, at most one
filter_tick call with a particular "type" argument will be
active at any time, and if there are no free slaves when a tick would
occur, the tick is skipped.

SUPPORTED VIRUS SCANNERS
The following virus scanners are supported by MIMEDefang:

o

OpenAntiVirus (http://www.openantivirus.org/) is supported in daemon-scanning
mode.

o

Symantec CarrierScan Server
(http://www.symantec.com/region/can/eng/product/scs/)

o

Trend Micro vscan (http://www.antivirus.com/)

o

Sophos Sweep (http://www.sophos.com/products/antivirus/savunix.html)

o

H+BEDV AntiVir (http://www.hbedv.com/)

o

Central Command Vexira (http://www.centralcommand.com/)

o

NAI uvscan (http://www.nai.com)

o

Bitdefender bdc (http://www.bitdefender.com)

o

Norman Virus Control (NVCC) (http://www.norman.no/)

o

Command csav (http://www.commandsoftware.com)

o

F-Secure fsav (http://www.f-secure.com)

o

The clamscan command-line scanner and the clamd daemon from
Clam AntiVirus (http://www.clamav.net/)

o

Kaspersky Anti-Virus (AVP) (http://www.kaspersky.com/)

o

F-Risk F-Prot (http://www.f-prot.com/)

o

F-Risk FPROTD (daemonized version of F-Prot)

o

Symantec CarrierScan Server (http://www.symantec.ca/region/can/eng/product/scs/buymenu.html)

o

The File::Scan Perl module (http://freshmeat.net/projects/filescan/)

o

Sophie (http://www.vanja.com/tools/sophie/), which uses the libsavi
library from Sophos, is supported in daemon-scanning mode.

o

Trophie (http://www.vanja.com/tools/trophie/), which uses the libvsapi
library from Trend Micro, is supported in daemon-scanning mode.

AUTHORS
mimedefang was written by David F. Skoll <dfs@roaringpenguin.com>.
The mimedefang home page is http://www.mimedefang.org/.

SEE ALSO
mimedefang(8), mimedefang.pl(8)