An alternative configuration file
can be specified using the
-C flag; for example,
sendmail -Ctest.cf -oQ/tmp/mqueue
uses the configuration file test.cf instead of the default /usr/lib/sendmail.cf. If the -C flag has no value it defaults to sendmail.cf in the current directory.
sendmail gives up its setuid root permissions when you use this flag, so it is common to use a publicly writable directory (such as /tmp) as the spool directory (QueueDirectory or Q option) while testing.