HP-UX Mailing Services Administrator's Guide

Mailing Services Overview
The Sendmail Utility
Chapter 1 37
• Temporary failures that have remained in the mail queue for the
queue timeout period (set with the Timeout.queuereturn option in
the /etc/mail/sendmail.cf file), which is normally five days.
• Local recipient user unknown.
• The recipient address cannot be resolved by the configuration file.
• Permanent delivery agent (mailer) failures.
• Inability to find an Internet address for a remote host.
• A remote SMTP server reports an address is undeliverable during
the SMTP transaction.
In most cases, if message delivery fails permanently on a remote system,
mail that includes a transcript of the failed delivery attempt and the
undelivered message is returned to the sender. This transcript includes
any standard error output from the delivery agent that failed.
If Sendmail tries all MX hosts in its preference list and fails to deliver a
message, the message is returned to the sender with an error message.
For more information, see “Mail Exchanger (MX) Records” on page 31.
If delivery failed on an alias, and an owner is configured for that alias in
the aliases database, Sendmail returns the message and transcript to the
alias owner.
If the message header contains an Errors-To: header line, Sendmail
returns the message and transcript to the address on the Errors-To:
line instead of to the sender’s address.
If the Postmaster Copy option (option P) is set to a valid address,
Sendmail sends a copy of the transcript and failed message (with the
message body deleted) to the Postmaster Copy address.
If the attempt to return the failed message itself fails, Sendmail returns
the message and transcript to the alias postmaster on the local system.
The postmaster alias in the default alias file
(/usr/newconfig/etc/mail/aliases) resolves to root.
If Sendmail is unable to return the message to any of the addresses
described previously, as a last resort it appends the error transcript and
returned message to the file /var/tmp/dead.letter.
Finally, if this fails, Sendmail logs the failure and leaves the original
failed message in the mail queue so that a future queue-processing
daemon will try to send it. If this fails, an error message is returned
again.