Installing and Administering Internet Services

182 Chapter4
Installing and Administering sendmail
How sendmail Works
sendmail then processes the message just as it did when it was
originally collected.
If sendmail detects, from the time stamp in a queued message, that the
message has been in the mail queue longer than the queue timeout, it
returns the message to the sender. The queue timeout is set with the
Timeout.queuereturn option in the /etc/mail/sendmail.cf file and,
by default, is five days.