If your MTA is sendmail, you should include the line

“| /usr/lib/mh/slocal -user username”

in your .forward file in your home directory. This will cause sendmail to invoke slocal on your behalf when a message arrives.

If your MTA is MMDF-I, you should (symbolically) link /usr/lib/mh/slocal to the file bin/rcvmail in your home directory. This will cause MMDF-I to invoke slocal on your behalf with the correct “address info sender” arguments.

If your MTA is MMDF-II, then you should not use slocal. An equivalent functionality is already provided by MMDF-II; see maildelivery(5) for details.

The “.maildelivery” file controls how slocal filters and delivers incoming mail. Each line of this file consists of five fields, separated by white-space or comma. Since double-quotes are honored, these characters may be included in a single argument by enclosing the entire argument in double-quotes. A double-quote can be included by preceding it with a backslash. Lines beginning with `#' and blank lines are ignored.

The format of each line in the “.maildelivery” file is:

header pattern action result string

header: The name of a header field (such as To, Cc, or From) that is to be searched for a pattern. This is any field in the headers of the message that might be present.

The following special fields are also defined:

source

the out-of-band sender information

addr

the address that was used to cause delivery to the recipient

default

this matches only if the message hasn't been delivered yet

*

this always matches

pattern: The sequence of characters to match in the specified header field. Matching is case-insensitive, but does not use regular expressions.

action: The action to take to deliver the message. When a message is delivered, a “Delivery-Date: date” header is added which indicates the date and time that message was delivered.

destroy

This action always succeeds. file, mbox, or > Append the message to the file named by string. The message is appended to the file in mbox (uucp) format. This is the format used by most other mail clients (such as mailx, elm). If the message can be appended to the file, then this action succeeds.

mmdf

Identical to file, but always appends the message using the MMDF mailbox format.

pipe or |

Pipe the message as the standard input to the command named by string, using the Bourne shell sh to interpret the string. Prior to giving the string to the shell, it is expanded with the following built-in variables:

$(sender)

the out-of-band sender information

$(address)

the address that was used to cause delivery to the recipient

$(size)

the size of the message in bytes

$(reply-to)

either the “Reply-To:” or “From:” field of the message

$(info)

the out-of-band information specified

qpipe or ^

Similar to pipe, but executes the command directly, after built-in variable expansion, without assistance from the shell. This action can be used to avoid quoting special characters which your shell might interpret.

folder or +

Store the message in the nmh folder named by string. Currently this is handled by piping the message to the nmh program rcvstore, although this may change in the future.

result: Indicates how the action should be performed:

A

Perform the action. If the action succeeds, then the message is considered delivered.

R

Perform the action. Regardless of the outcome of the action, the message is not considered delivered.

?

Perform the action only if the message has not been delivered. If the action succeeds, then the message is considered delivered.

N

Perform the action only if the message has not been delivered and the previous action succeeded. If this action succeeds, then the message is considered delivered.

The delivery file is always read completely, so that several matches can be made and several actions can be taken.

In order to prevent security problems, the “.maildelivery” file must be owned either by the user or by root, and must be writable only by the owner. If this is not the case, the file is not read.

If the “.maildelivery” file cannot be found, or does not perform an action which delivers the message, then slocal will check for a global delivery file at /etc/nmh/maildelivery. This file is read according to the same rules. This file must be owned by the root and must be writable only by the root.

If a global delivery file cannot be found or does not perform an action which delivers the message, then standard delivery to the user's maildrop is performed.

To summarize, here's an example delivery file:

#
# .maildelivery file for nmh's slocal
#
# Blank lines and lines beginning with a '#' are ignored
#
# FIELD   PATTERN   ACTION  RESULT  STRING
#

# File mail with foobar in the “To:” line into file foobar.log To foobar file A foobar.log

# Pipe messages from coleman to the program message-archive From coleman pipe A /bin/message-archive

# Anything to the “nmh-workers” mailing list is put in # its own folder, if not filed already To nmh-workers folder ? nmh-workers

# Anything with Unix in the subject is put into # the file unix-mail Subject unix file A unix-mail

# I don't want to read mail from Steve, so destroy it From steve destroy A -

# Put anything not matched yet into mailbox default - file ? mailbox

# always run rcvtty * - pipe R /usr/lib/mh/rcvtty

When a process is invoked, its environment is: the user/group-ids are set to recipient's ids; the working directory is the recipient's home directory; the umask is 0077; the process has no /dev/tty; the standard input is set to the message; the standard output and diagnostic output are set to /dev/null; all other file-descriptors are closed; the environment variables $USER, $HOME, $SHELL are set appropriately, and no other environment variables exist.

The process is given a certain amount of time to execute. If the process does not exit within this limit, the process will be terminated with extreme prejudice. The amount of time is calculated as ((size / 60) + 300) seconds, where size is the number of bytes in the message (with 30 minutes the maximum time allowed).

The exit status of the process is consulted in determining the success of the action. An exit status of zero means that the action succeeded. Any other exit status (or abnormal termination) means that the action failed.

In order to avoid any time limitations, you might implement a process that began by fork()-ing. The parent would return the appropriate value immediately, and the child could continue on, doing whatever it wanted for as long as it wanted. This approach is somewhat risky if the parent is going to return an exit status of zero. If the parent is going to return a non-zero exit status, then this approach can lead to quicker delivery into your maildrop.