-The first way is GECOS\-based username masquerading. If the \*(lqmasquerade:\*(rq line
-in
-.I mts.conf
-contains \*(lqmmailid\*(rq, this processing is activated. If a user's GECOS
-field in the passwd file is of the form \*(lqFull Name <fakename>\*(rq then \*(lqfakename\*(rq
-will be used in place of the real username. For instance, a GECOS field of \*(lqDan
-Harkless <Dan.Harkless>\*(rq would result in \*(lqFrom: Dan Harkless
-<Dan.Harkless@machine.example.com>\*(rq. Naturally if you were doing something like
-this you'd want to set up an MTA alias (e.g. in /etc/aliases) from, for
-instance, \*(lqDan.Harkless\*(rq to \*(lqdan\*(rq.
-.PP
-The second way to override default construction of \*(lqFrom:\*(rq is to set the
-.B $SIGNATURE
-environment variable. This variable overrides the full name
-from the GECOS field, even if GECOS\-based masquerading is being done. This
-processing is always active, and does not need to be enabled from
-.IR mts.conf .
-.PP
-The third way is controlled by the \*(lquser_extension\*(rq value of \*(lqmasquerade:\*(rq line
-of
-.IR mts.conf .
-When that's turned on, setting the
-.B $USERNAME_EXTENSION
-environment variable will result in its value being appended the user's login
-name. For instance, if I set
-.B $USERNAME_EXTENSION
-to \*(lq+www\*(rq, my \*(lqFrom:\*(rq
-line will contain \*(lqDan Harkless <dan+www@machine.example.com>\*(rq (or
-\*(lqDan.Harkless+www\*(rq if I'm using mmailid masquerading as well). Recent versions
-of
-.B sendmail
-automatically deliver all mail sent to
-.IR user + string
-to
-.IR user .
-.B qmail
-has a similar feature which uses '\-' as the delimiter by
-default, but can use other characters as well.
+The first way is to supply a \*(lqSender:\*(rq line. The value of this
+field will be used as the originating mailbox identity when submitting the
+message to the mail transport system. If multiple addresses are
+given in the \*(lqFrom:\*(rq line, a \*(lqSender:\*(rq line is
+.BR required .
+If an \*(lqEnvelope-From:\*(rq line is supplied when multiple addresses
+are given in the \*(lqFrom:\*(rq line, a \*(lqSender:\*(rq header will
+be generated using the value of the \*(lqEnvelope-From:\*(rq line,
+.B if
+the \*(lqEnvelope-From:\*(rq line is not blank.