freebsd man page for mailwrapper

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

NAME
     mailwrapper -- invoke appropriate MTA software based on configuration file

SYNOPSIS
     Special.  See below.

DESCRIPTION
     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 sys-
     tem 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
     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 configura-
     tion information placed in ${LOCALBASE}/etc/mail/mailer.conf falling back on /etc/mail/mailer.conf.  This permits the administrator to con-
     figure 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.

FILES
     Configuration for mailwrapper is kept in ${LOCALBASE}/etc/mail/mailer.conf or /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.

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

DIAGNOSTICS
     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.

SEE ALSO
     mail(1), mailq(1), newaliases(1), mailer.conf(5), periodic.conf(5), sendmail(8)

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

AUTHORS
     Perry E. Metzger <perry@piermont.com>

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

BSD
								  August 27, 2014							       BSD