.\"	$OpenBSD: mailwrapper.8,v 1.1 1999/08/02 19:50:07 jakob Exp $
.\"	$NetBSD: mailwrapper.8,v 1.5 1999/03/22 18:44:01 garbled Exp $
.\"
.\" Copyright (c) 1998
.\" 	Perry E. Metzger.  All rights reserved.
.\"
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.\"	by Perry E. Metzger.
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.Dd December 16, 1998
.Dt MAILWRAPPER 8
.Os
.Sh NAME
.Nm mailwrapper
.Nd invoke appropriate MTA software based on configuration file
.Sh SYNOPSIS
Special. See below.
.Sh DESCRIPTION
At one time, the only Mail Transfer Agent (MTA) software easily available
was
.Xr sendmail 8 .
As a result of this, most Mail User Agents (MUAs) such as
.Xr mail 1
had the path and calling conventions expected by
.Xr sendmail 8
compiled in.
.Pp
Times have changed, however.
On a modern system, the administrator may wish to use one of several
available MTAs.
.Pp
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
.Xr sendmail 8
and may be put into place instead of
.Xr sendmail 8
in
.Pa /usr/sbin/sendmail .
.Pp
.Xr sendmail 8
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 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
.Xr sendmail 8
helps in installing alternative MTAs, it essentially makes the
configuration of the system depend on hard installing new programs in
.Pa /usr .
This leads to configuration problems for many administrators, since
they may wish to install a new 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 MTA instead of
.Xr sendmail 8
based on configuration information placed in
.Pa /etc/mailer.conf .
This permits the administrator to configure which 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 DIAGNOSTICS
.Nm
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
.Nm
was invoked.
.Sh SEE ALSO
.Xr mail 1 ,
.Xr mailq 1 ,
.Xr newaliases 1 ,
.Xr mailer.conf 5 ,
.Xr sendmail 8
.Sh AUTHORS
Perry E. Metzger <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 "behave
differently if invoked with a different name" behavior of things like
.Xr mailq 1
should go away.