HP-UX Mailing Services Administrator's Guide

Mailing Services Overview
The Sendmail Utility
Chapter 136
mailclient. (The Sendmail installation script sets the DH macro value to
the host specified by SENDMAIL_SERVER_NAME.) Outgoing mail that is not
local is sent by mailclient to the remote host using MX records. Because
the DM macro entry in the /etc/mail/sendmail.cf file on mailclient is
set to mailserv.company.com, mail from user1 appears to be from
[e-mail].
Because mail sent to remote hosts from user1 is sent from
[e-mail], replies to user1’s messages are
returned to mailserv. On mailserv, when Sendmail receives mail for
user1, it looks up user1 in the aliases database and redirects mail for
user1 to user1@mailclient.
You can modify Sendmail server and client operations. Most
modifications involve changing or re-creating the
/etc/mail/sendmail.cf file on the server or client systems. For
example, you can define the DM macro on a mail server system. You can
also modify the /etc/mail/sendmail.cf file so that the clients relay all
outbound mail to the server; this is described in “Modifying the Default
Sendmail Configuration File” on page 48.
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: