NAME

mail_pipe - invoke recipient command for incoming mail

SYNOPSIS

mail_pipe [ -x debug_level ] -r recipient -R  path_to_sender
-c content_type -S subject

DESCRIPTION

When a new mail message arrives, the mail command first checks if the recipient's mailbox indicates that the message is to be forwarded elsewhere (to some other recipient or as the input to some command). If the message is to be piped into a recipient-specified command, mail invokes mail_pipe to do some validation and then execute the command in the context of the recipient.

Command-line arguments are:
-x debug_level    Turn on debugging for this invocation. See
                  the  description  of the -x option for the
                  mail command for details.
-r recipient      The recipient's login id.
-R path_to_sender The return address to the message's origi-
                  nator.
-c content_type   The value of the Content-Type: header line
                  in the message.
-S subject        The value of the Subject: header  line  in
                  the message if present.

mail_pipe is installed as a setuid-to-root process, thus enabling itself to change it's user and group ids to that of the recipient as necessary.

When invoked, mail_pipe performs the following steps  (if  a
step fails, the exit code is noted as [N]):
-  Validate invocation arguments [1].
-  Verify that recipient name is < 14 characters long [2].
-  Verify that the setgid flag for the recipient mailbox  is
   set [3].
-  Open /var/mail/recipient [4].
-  Verify that recipient's mailbox starts  with  the  string
   Forward to [5].
-  Find pipe symbol indicating start of  command  string  in
   recipient mailbox [6].
-  Find entry for recipient in /etc/passwd [7].
-  Set gid to recipient's gid [8].
-  Set uid to recipient's uid [9].
-  Change current directory to recipient's  login  directory
   [10].
-  Allocate space to  hold  newly  exec'ed  environment  for
   recipient command [11].
-  Parse the  recipient  command,  performing  any  %keyword
   expansions  required.   See the `Forwarding mail' section
   of mail(1), for more information regarding %keyword  sub-
   stitutions [12].
-  Execute recipient command [13 if  exec  fails,  otherwise
   exit code from recipient command itself].

FILES

/etc/passwd      to identify sender and locate recipients
/var/mail/recipient
                 incoming mail for recipient; that  is,  the
                 mail file
/tmp/MLDBG*      debug trace file
/usr/lib/mail/mail_pipe
                 mail_pipe program

SEE ALSO

mail(1), notify(1), vacation(1)