Over the weekend I gave the smtpinvite thing that I found on TechTV’s server a try. The idea is that the primary MX will always defer people – it exist solely for adding sending hosts to a whitelist – when the remote MTA then goes to the secondary it will let the mail through.
This works fine for most MTA’s that I looked at during the few hours I had it up. Sendmail however will not contact the secondaries when it gets a defer message it will just keep trying to talk to the primary on each retry! Surely that is wrong, I have not gone to study the RFC’s but it seems very stupid to me. So unfortunately I had to abandon the idea.
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