HP-UX Mailing Services Administrator's Guide (B2355-91064)

How Sendmail Handles Errors
By default, Sendmail immediately reports to standard output any errors that occur
during the routing or delivery of a message. Sendmail distinguishes between temporary
failures and permanent failures.
Permanent failures are mail transactions that are unlikely to succeed without the
intervention of the sender or a system administrator. For example, mailing to an
unknown user is a permanent failure. A delivery failure of the local mailer because the
file system is full is also a permanent failure.
Temporary failures are mail transactions that might succeed if retried later. For example,
an error message connection refused displayed while attempting to connect to a
remote SMTP server is a temporary failure, since it probably means that the server is
temporarily not running on the remote host.
How Sendmail Handles Permanent Failures
Permanent failures include the following:
• 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” (page 27).
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.
34 Mailing Services Overview