MAILWRAPPER(8) BSD System Manager's Manual MAILWRAPPER(8)NAMEmailwrapper — invoke appropriate MTA software based on configuration file
Special. See below.
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)
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
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 drop-in replacements for 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 configura‐
tion 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 sys‐
tem 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 adminis‐
trator 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.
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.
The mailwrapper utility exits 0 on success, and >0 if an error occurs.
The 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 ALSOmail(1), mailq(1), newaliases(1), mailer.conf(5), periodic.conf(5),
The mailwrapper utility first appeared in NetBSD 1.4 and then
Perry E. Metzger ⟨email@example.com⟩
The entire reason this program exists is a crock. Instead, a command for
how to submit mail should be standardized, and all the "behave differ‐
ently if invoked with a different name" behavior of things like mailq(1)
should go away.
BSD August 7, 2006 BSD