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

     mailwrapper -- invoke appropriate MTA software based on configuration

     Special.  See below.

     At one time, the only Mail Transfer Agent (MTA) software easily available
     was sendmail(8).  As a result of this, most Mail User Agents (MUAs) such
     as mail(1) had the path and calling conventions expected by sendmail(8)
     compiled in.

     Times have changed, however.  On a modern UNIX 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 so that they use the same calling
     conventions as sendmail(8) and may be put into place instead of
     sendmail(8) in /usr/sbin/sendmail.

     sendmail(8) 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(8) helps
     in installing alternative MTAs, it essentially makes the configuration of
     the system depend on hard 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 utility is designed to replace /usr/sbin/sendmail and to
     invoke an appropriate MTA instead of sendmail(8) based on configuration
     information placed in /etc/mail/mailer.conf.  This permits the adminis-
     trator to configure which MTA is to be invoked on the system at run time.

     Other configuration files may need to be altered when replacing
     sendmail(8).  For example, if the replacement MTA does not support the -A
     option with mailq(1), daily_status_include_submit_mailq should be turned
     off in /etc/periodic.conf.

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

     The mailwrapper utility will return an error value and print a diagnostic
     if its configuration file is missing or malformed, or does not contain a
     mapping for the name under which mailwrapper was invoked.

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

     The mailwrapper utility first appeared in NetBSD 1.4 and then
     FreeBSD 4.0.

     Perry E. Metzger <perryATpiermont.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 differ-
     ently if invoked with a different name" behavior of things like mailq(1)
     should go away.

BSD                            December 16, 1998                           BSD