The
Smail 3.x program (a UUCP-oriented replacement
for sendmail) produces an
Apparently-From: header when it is unable to find
any of the official sender headers in a mail message. The address
that it provides to this nonstandard header is taken from the
envelope of the message.
The sendmail program, on the other hand, places
the envelope sender into a From: header in this
situation. If there is no envelope sender and if the sender was not
specified in the command line, sendmail sets the
sender to be the postmaster.
The Apparently-From: header is mentioned here only
because it can appear in messages received at sites that run
sendmail. It shouldn't cause
problems because a good sender address still appears in the SMTP
envelope.
The Apparently-From: header should never be
declared in the configuration file and should not be added to
conf.c.
