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 replacement programs that plug replace sendmail(8) 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 utility is designed to
replace /usr/sbin/sendmail and to invoke an
appropriate MTA instead of
sendmail(8) based on configuration information placed in
/etc/mail/mailer.conf. This permits the
administrator to configure 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
/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 utility will print a
diagnostic if its configuration file is malformed or does not contain a
mapping for the name under which mailwrapper was
invoked. In case the configuration file does not exist at all, a syslog
event is being generated and mailwrapper falls back
to the default mailer, which is
sendmail(8).
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 differently if invoked with a different name" behavior of things like mailq(1) should go away.