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

SMTP Addresses:
RFC 2822-style addresses in any of the following forms, where host is not the local
host name, are routed by SMTP over TCP/IP:
user@host
[e-mail]
<@host,@host2,@host3:user@host4>
user@[remote_host’s_internet_address]
If the name server is in use, Sendmail requests mail exchanger (MX) records for the
remote host. If there are any, it attempts to deliver the mail to each of them, in the order
of preference, until delivery succeeds.
Otherwise, Sendmail connects directly to the recipient host and delivers the message.
Mixed Addresses:
The supplied configuration file interprets address operators with the following
precedence:
@, !, %
This means that recipient addresses using mixtures of these operators are resolved as
shown in Table 1-3.
Table 1-3 How Sendmail Resolves Addresses with Mixed Operators
RecipientUserHostMailerAddress
user@hostAuser%hostA@hostBhostB
TCP
user%hostA@hostB
hostA!userhostA!user@hostBhostB
TCP
user!hostA@hostB
user@hostBuser@hostBhostA
UUCP
hostA!user%hostB
Mail Exchanger (MX) Records
The BIND name server, if it is in use on your host, provides MX records. These can be
used to notify Sendmail that mail for a particular host can be relayed by another host,
if the addressed host is temporarily down or otherwise inaccessible. For information
on creating MX records, see HP-UX IP Address and Client Management Guide at:
http://www.docs.hp.com/hpux/netcom/index.html#Internet%20Services
MX records are used only if a message address resolves to an IPC mailer (that is, one
that uses SMTP over sockets to perform delivery). Instead of attempting to connect
directly to the recipient host, Sendmail first queries the name server, if it is running,
for MX records for that host. If the name server returns any answer, Sendmail sorts them
in preference order, highest preference (lowest number) first. If the local host appears
in the list, the local host and any MX hosts with lower preference (higher numbers) are
removed from the list. If any MX hosts remain, Sendmail then tries to connect to each
The Sendmail Utility 27