mailwrapper man page on FreeBSD

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

     mailwrapper — invoke appropriate MTA software based on configuration file

     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 drop-in replacements for sendmail(8) helps in installing
     alternative MTAs, it essentially makes the configuration of the system
     depend on hand installing new programs in /usr.  This leads to configura‐
     tion 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 sys‐
     tem 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 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 exits 0 on success, and >0 if an error occurs.

     The 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), mailer.conf(5), periodic.conf(5),

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

     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 differ‐
     ently if invoked with a different name" behavior of things like mailq(1)
     should go away.

BSD				August 7, 2006				   BSD

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