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We have a Windows 2008 SP2 DNS server configured to use root hints. We have a certain MX record lookup that it periodically fails to resolve for our client machines.

The lookup is for the MX record for mydomain.com, which should resolve to mydomain-com.mail.eo.outlook.com.

Periodically our DNS server returns SERVFAIL error indicating it cant resolve the A record for mydomain-com.mail.eo.outlook.com.

From my research, it appears to be related to the different TTL values of the MX record, and the A record. The MX record has a TTL of 3600, the A record has a TTL of 60.

Has anyone experienced this issue before? Where the A record expires before the CNAME does, and causes your DNS server to return SERVFAIL error when attempting to resolve a MX record? Various technet articles recommend either enabling DNS forwarders, or decreasing your MaxCacheTTL entry. I simply dont understand why these would correct the issue? Why would the DNS server not just use root hints to lookup the A record again?

LINK: Technet article describing similar issue

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