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NetBSD 6.1.5 - man page for mailwrapper (netbsd section 8)

MAILWRAPPER(8)			   BSD System Manager's Manual			   MAILWRAPPER(8)

     mailwrapper -- invoke appropriate MTA software based on configuration file

     Special. See below.

     Once upon time, the only Mail Transfer Agent (MTA) software easily available was
     ``sendmail''.  This famous MTA was written by Eric Allman and first appeared in 4.1BSD.  The
     legacy of this MTA affected most Mail User Agents (MUAs) such as mail(1); the path and call-
     ing conventions expected by ``sendmail'' were compiled in.

     But times changed.  On a modern NetBSD system, the administrator may wish to use one of sev-
     eral available MTAs.

     It would be difficult to modify all MUA software typically available on a system, so most of
     the authors of alternative MTAs have written their front end message submission programs
     that may appear in the place of /usr/sbin/sendmail, but still follow the same calling con-
     ventions as ``sendmail''.

     The ``sendmail'' MTA also typically has aliases named mailq(1) and newaliases(1) linked to
     it.  The program knows to behave differently when its argv[0] is ``mailq'' or ``newaliases''
     and behaves appropriately.  Typically, replacement MTAs provide similar functionality,
     either through a program that also switches behavior based on calling name, or through a set
     of programs that provide similar functionality.

     Although having replacement programs that plug replace ``sendmail'' helps in installing
     alternative MTAs, it essentially makes the configuration of the system depend on hand
     installing new programs in /usr.  This leads to configuration problems for many administra-
     tors, since they may wish to install a new MTA without altering the system provided /usr.
     (This may be, for example, to avoid having upgrade problems when a new version of the system
     is installed over the old.)  They may also have a shared /usr among several machines, and
     may wish to avoid placing implicit configuration information in a read-only /usr.

     The mailwrapper program is designed to replace /usr/sbin/sendmail and to invoke an appropri-
     ate MTA based on configuration information placed in /etc/mailer.conf.  This permits the
     administrator to configure which MTA is to be invoked on the system at run time.

     mailwrapper exits 0 on success, and >0 if an error occurs.

     Configuration for mailwrapper is kept in /etc/mailer.conf.  /usr/sbin/sendmail is typically
     set up as a symlink to mailwrapper which is not usually invoked on its own.

     mailwrapper will print a diagnostic if its configuration file is missing or malformed, or
     does not contain a mapping for the name under which it was invoked.

     mail(1), mailq(1), newaliases(1), postfix(1), mailer.conf(5)

     The mailwrapper program appeared in NetBSD 1.4.

     Perry E. Metzger <perry@piermont.com>

     The entire reason this program exists is a crock.	Instead, a command for how to submit mail
     should be standardized, and all the ``behave differently if invoked with a different name''
     behavior of things like mailq(1) should go away.

BSD					  April 10, 2010				      BSD

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