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Another one to avoid is using a CNAME in the MX. It will work until it doesn't.
by scandox 6y ago
Another one to avoid is using a CNAME in the MX. It will work until it doesn't.
- t0mas88 6y agoJup 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.
- lucb1e 6y agoDoing a mail server project, you don't want to know how many people have recursive cnames configured on their mx records. At least now I know that ruby has a stack size of over ten thousand.