relay=
The host that sent or accepted the message syslog equate
When running as a daemon and listening for incoming
connections, sendmail attempts
to look up the true identity of connecting users and
hosts. When it can find that information, it saves
it in the $_
sendmail macro ($_ on page 801).
When transporting mail to other hosts, sendmail looks up the MX records for those hosts and connects to the MX records when they are available. If MX records are not available, sendmail connects to A or AAAA addresses.
For recipient and sender syslog
lines, the relay=
syslog equate shows the name of
the corresponding receiving or sending host,
followed by the A address, or AAAA address, of that
host (if there was one) in square braces:
relay=root@other.site.edu [123.45.67.89]
If the sender is a local user, the login name and
localhost will appear in the
relay=
syslog equate:
relay=bob@localhost
In summary, the relay=
syslog equate shows who
really accepted or sent the
message.
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