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Jup that one looks like it works for basic test cases but then breaks unexpectedly in the real world. Can't remember the exact problem but I have remembered to
by t0mas88 6y ago
Jup that one looks like it works for basic test cases but then breaks unexpectedly in the real world. Can't remember the exact problem but I have remembered to never point MX at a CNAME.
- JdeBP 6y agoThe SMTP standard specifies a loop prevention algorithm that ensures that fallback SMTP Relay servers don't end up forwarding back to themselves or even their own fallback servers. This loop prevention relies upon looking at the domain names in the MX resource records, and breaks if such a name is an (unknown by the fallback server itself) alias for the true domain name via a CNAME resource record.