30.5.1 The *file* and *include* Agents

The *file* delivery agent (the * characters are part of the name) handles delivery to files. The *include* delivery agent handles delivery through :include: lists. Neither can be considered a real delivery agent, because actual delivery is still handled internally by sendmail. Instead, they provide a way to tune delivery-agent behavior for these two delivery needs.

The predefined defaults for these delivery agents can be viewed with the following command: [13]

[13] The output lines are unfortunately wrapped at the right margin of this book text.

% /usr/lib/sendmail -d0.15 -bt < /dev/null | egrep "file|include" 
mailer 1 (*file*): P=[FILE] S=0/0 R=0/0 M=0 U=0:0 F=9DEFMPloqsu L=0 E=\n T=DNS/RF
C822/X-Unix A=FILE $u
mailer 2 (*include*): P=/dev/null S=0/0 R=0/0 M=0 U=0:0 F=su L=0 E=\n T=<undefine
d>/<undefined>/<undefined> A=INCLUDE $u

The defaults may be overwritten by declaring these delivery agents in the configuration file. For example, the following configuration file declaration overrides the internal definition shown above, and limits the size of any mail message that is delivered to files to 1 megabyte:

M*file*, P=[FILE], M=1000000, F=9DEFMPloqsu, T=DNS/RFC822/X-Unix, A=FILE $u

Note that any equate that does not default to zero (such as the P=, F=, T=, and A= equates) needs to be copied to this configuration file declaration, or the original value will be lost.

A similar change in definition for the m4 configuration of V8 sendmail would look like this:

LOCAL_CONFIG
M*file*, P=[FILE], M=1000000, F=9DEFMPloqsu, T=DNS/RFC822/X-Unix, A=FILE $u

30.5.2 The error Delivery Agent

All versions of sendmail define a special internal delivery agent called error that is designed to aid in the issuance of error messages. It is always available for use in rule sets 0 and 5, and the check_... rule sets and cannot be defined with an M command.

Beginning with V8.7, the form for using the error agent in the RHS of a rule looks like this:

R...          $#error $@ dsn  $: text of error message here

In general terms, the text following the $: is the actual error message that will be included in bounced mail and sent back to a connecting SMTP host. For example, the following rule in rule set 0 would cause all mail to the local user George Washington to bounce:

RGeorge.Washington       $#error $: George Washington doesn't sleep here anymore

with an error message like this:

553 <george.washington>... George Washington doesn't sleep here anymore

30.5.3 The $: Part

Recall that the text of the error message following the $: is used as a literal error message. That is, this $: part:

R...          $#error  $: george doesn't sleep here anymore

produces this error for the address [email protected]:

553 <[email protected]>... george doesn't sleep here anymore

Here the 553 is an SMTP code (see RFC821). If you want a different SMTP code issued, you may do so by prefixing the $: part with it:

R...          $#error  $: 421 george doesn't sleep here anymore

If three digits followed by a space are present as a prefix, those digits are used as the SMTP reply code when sendmail is speaking SMTP. If no digits and space prefix the text, the default SMTP reply code is 553.

A few SMTP codes that are useful with $: are listed in Table 30.7. The complete list of all SMTP codes can be found in RFC821.

Note that you should restrict yourself to the small set of codes that may legally be returned to the RCPT SMTP command. Also note that any DSN code that is specified in the $@ part must avoid conflicting with the meaning of the SMTP code. For example, the following construct is wrong and should be avoided:

R...          $#error $@ 2.1.1 $: 553 ...      avoid such conflicts

Here, the DSN 2.1.1 means that delivery was successful, whereas the SMTP 553 means that delivery failed and the message bounced.