Why does Exim say all relevant MX records point to non-existent hosts when MX records point to IP addresses?

MX records cannot point to IP addresses. They are defined to point to host names, so Exim always interprets them that way. (An IP address is a syntactically valid host name.) The DNS for the domain you are having problems with is misconfigured. However, it appears that more and more DNS zones are breaking the rules and putting IP addresses on the RHS of MX records. Exim follows the rules and rejects this, but other MTAs do support it, so the allow_mx_to_ip was regretfully added at release 3.14 to permit this heinous activity.

See also: http://wiki.debian.org/PkgExim4UserFAQ#head-c07978cdc8abc5ab0fffd980a23f87c8b34dc983

• there may be rules ignoring hosts on the local network (e.g. 192.168.0.0/16).

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