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

     mailwrapper -- invoke appropriate MTA software based on configuration

     Special.  See below.

     Once upon time, the only Mail Transfer Agent (MTA) software easily avail-
     able 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 calling conventions expected
     by ``sendmail'' were compiled in.

     But times changed.  On a modern NetBSD system, the administrator may wish
     to use one of several 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 conventions as

     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 administrators, 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 configura-
     tion information in a read-only /usr.

     The mailwrapper program is designed to replace /usr/sbin/sendmail and to
     invoke an appropriate 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.

     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.

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

     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 <>

     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.

NetBSD 8.0                      April 10, 2010                      NetBSD 8.0

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