|MAILWRAPPER(8)||System Manager's Manual||MAILWRAPPER(8)|
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 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(8) and newaliases(8) 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 hard 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.
mailwrapper program is designed to
replace /usr/sbin/sendmail and to invoke an
appropriate MTA instead of sendmail(8)
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.
mailwrapperis kept in /etc/mailer.conf. /usr/sbin/sendmail is typically set up as a symlink to
mailwrapperwhich is not usually invoked on its own.
mailwrapperwill invoke smtpd(8) 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
|December 14, 2015||OpenBSD-current|