xref: /netbsd-src/usr.sbin/mailwrapper/mailwrapper.8 (revision 597b141c6c760f590b089660f98f164ddc804595)

.\"	$NetBSD: mailwrapper.8,v 1.18 2017/07/04 07:10:35 wiz Exp $
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.\" Copyright (c) 1998
.\" 	Perry E. Metzger.  All rights reserved.
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.Dd April 10, 2010
.Dt MAILWRAPPER 8
.Os
.Sh NAME
.Nm mailwrapper
.Nd invoke appropriate
.Tn MTA
software based on configuration file
.Sh SYNOPSIS
Special.
See below.
.Sh DESCRIPTION
Once upon time, the only Mail Transfer Agent
.Pq Tn MTA
software easily available was
.Dq sendmail .
This famous
.Tn MTA
was written by
.An Eric Allman
and first appeared in
.Bx 4.1 .
The legacy of this
.Tn MTA
affected most Mail User Agents
.Pq Tn MUAs
such as
.Xr mail 1 ;
the path and calling conventions expected by
.Dq sendmail
were compiled in.
.Pp
But times changed.
On a modern
.Nx
system, the administrator may wish to use one of several available
.Tn MTAs .
.Pp
It would be difficult to modify all
.Tn MUA
software typically available on a system,
so most of the authors of alternative
.Tn MTAs
have written their front end message submission programs
that may appear in the place of
.Pa /usr/sbin/sendmail ,
but still follow the same calling conventions as
.Dq sendmail .
.Pp
The
.Dq sendmail
.Tn MTA
also typically has aliases named
.Xr mailq 1
and
.Xr newaliases 1
linked to it.
The program knows to behave differently when its
.Va argv[0]
is
.Dq mailq
or
.Dq newaliases
and behaves appropriately.
Typically, replacement
.Tn 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.
.Pp
Although having replacement programs that plug replace
.Dq sendmail
helps in installing alternative
.Tn MTAs ,
it essentially makes the configuration of the system depend
on hand installing new programs in
.Pa /usr .
This leads to configuration problems for many administrators, since
they may wish to install a new
.Tn MTA
without altering the system provided
.Pa /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
.Pa /usr
among several machines, and may wish to avoid placing
implicit configuration information in a read-only
.Pa /usr .
.Pp
The
.Nm
program is designed to replace
.Pa /usr/sbin/sendmail
and to invoke an appropriate
.Tn MTA
based on configuration information placed in
.Pa /etc/mailer.conf .
This permits the administrator to configure which
.Tn MTA
is to be invoked on the system at run time.
.Sh FILES
Configuration for
.Nm
is kept in
.Pa /etc/mailer.conf .
.Pa /usr/sbin/sendmail
is typically set up as a symlink to
.Nm
which is not usually invoked on its own.
.Sh EXIT STATUS
.Ex -std
.Sh DIAGNOSTICS
.Nm
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.
.Sh SEE ALSO
.Xr mail 1 ,
.Xr mailq 1 ,
.Xr newaliases 1 ,
.Xr postfix 1 ,
.Xr mailer.conf 5
.Sh HISTORY
The
.Nm
program appeared in
.Nx 1.4 .
.Sh AUTHORS
.An Perry E. Metzger Aq Mt perry@piermont.com
.Sh BUGS
The entire reason this program exists is a crock.
Instead, a command
for how to submit mail should be standardized, and all the
.Dq behave differently if invoked with a different name
behavior of things like
.Xr mailq 1
should go away.