NAME

mailwrapper — invoke appropriate MTA software based on configuration file

SYNOPSIS

Special. See below.

DESCRIPTION

Once upon time, the only Mail Transfer Agent (MTA) software easily available was “sendmail”. This famous MTA was written by Eric Allman and first appeared in 4.1BSD. The legacy of this MTA affected most Mail User Agents (MUAs) such as mail(1); the path and calling conventions expected by “sendmail” were compiled in.

But times changed. On a modern NetBSD 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 that may appear in the place of /usr/sbin/sendmail, but still follow the same calling conventions as “sendmail”.

The “sendmail” MTA 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” helps in installing alternative MTAs, it essentially makes the configuration of the system 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 program is designed to replace /usr/sbin/sendmail and to invoke an appropriate MTA based on configuration information placed in /etc/mailer.conf. This permits the administrator to configure which MTA is to be invoked on the system at run time.

EXIT STATUS

mailwrapper exits 0 on success, and >0 if an error occurs.

FILES

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

DIAGNOSTICS

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), postfix(1), mailer.conf(5)

HISTORY

The mailwrapper program appeared in NetBSD 1.4.

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 differently if invoked with a different name” behavior of things like mailq(1) should go away.