MAILWRAPPER(8) BSD System Manager's Manual MAILWRAPPER(8)NAMEmailwrapper — invoke appropriate MTA software based on configuration file
SYNOPSIS
Special. See below.
DESCRIPTION
Once upon time, the only Mail Transfer Agent (MTA) software easily avail‐
able 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. Typi‐
cally, 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 configura‐
tion 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 STATUSmailwrapper 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.
DIAGNOSTICSmailwrapper 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 ALSOmail(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.
BSD April 10, 2010 BSD