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...ect address feature of the domain routing table and avoid looking up MX RRs altogether. After all, if the mail arrived here it is a good bet that the main MX is off-line (or this is SPAM/UCEM but that is another issue). So assuming that the primary MX host is mx10.example.com and the secondary is mx40.something.else then with Sendmail the file /etc/mail/mailertable on mx40.something.else should contain something like this: example.com. esmtp:[mx10.example.com] .example.com. esmtp:[mx10.example.com] The [] brackets prevent MX lookups and just routes the message traffic directly to mx10.example....