invoke appropriate MTA software based on
Special. See below.
At one time, the only Mail Transfer Agent (MTA) software easily available was
. As a result of
this, most Mail User Agents (MUAs) such as
had the path and calling
conventions expected by
Times have changed, however. On a modern 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
and may be put
into place instead of
also typically has
aliases named mailq(8)
linked to it.
The program knows to behave differently when its
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
installing alternative MTAs, it essentially makes the configuration of the
system depend on hard installing new programs in
. 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
among several machines, and may wish to
avoid placing implicit configuration information in a read-only
program is designed to replace
and to invoke an appropriate
MTA instead of sendmail(8)
based on configuration information placed in
. This permits the administrator
to configure which MTA is to be invoked on the system at run time.
Configuration for mailwrapper
is kept in
is typically set up as a
symlink to mailwrapper
which is not usually
invoked on its own.
if its configuration
file is missing. It will return an error value and print a diagnostic if its
configuration file is malformed, or does not contain a mapping for the name
under which mailwrapper
Perry E. Metzger
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
should go away.