The initial behavior of sendmail is determined
largely by the command line used to invoke it. The command line can,
for example, cause sendmail to use a different
configuration file or to rebuild the aliases
file rather than deliver mail. The command line can be typed at your
keyboard, executed from a boot-time script, or even executed by an
MUA when sending mail.
The format of the sendmail command line is:
argv switches recipients
Here, argv is the name used to run
switches, if any are present, must always
precede the list of recipients. The
recipients is a list of zero or more
recipient address expressions.