Sometimes it is desirable to have vacation mail resemble bounced email. One way to accomplish this is to use the -z command-line switch. That switch causes the vacation message to appear to come from the special user "<>" instead of from you. At the original sender's end, the message will likely appear to come from MAILER-DAEMON or something similar:

From MAILER-DAEMON@your.domain  Sat Jan  1 19:56:21 2000

As a side effect, the vacation reply will also have this header added:

X-Authentication-Warning: local.domain:  you set sender to <> using -f

This -z command-line switch is useful if your vacation messages generate significant bounced mail. This could be the case if you get lots of spam email, for example. Using this -z command-line switch will prevent vacation messages to those bad reply addresses from bouncing:

|"/usr/ucb/vacation -z you"