Exchange unable to send emails – DNS doesn’t resolve on Windows 2xxx :)

Time to time, I see situations, when Exchange unable to send some emails to some organisations. In most cases, there is not a problem on Exchange level. Very often, it’s is DNS issues. If you check your logs, you can find there some events with similar content:
The DNS server encountered an invalid domain name in a packet from The packet will be rejected. The event data contains the DNS packet.

Here is a solution that works for me :).

Check following registry key and value set for it:

According to KB 198410 it should have a non-zero value
The packet was forwarded to non-recursive DNS server. I will recommend switch to forwarders for few days to check if that helps.
The server is querying for DNAME record, which is not supported. Responses containing DNAME (rrtype – 0×0027) record.
Extended DNS (EDNS) packets are received but the server that is attempting to resolve the EDNS traffic doesn’t support EDNS or have it enabled. An easy workaround is to disable EDNS.

Written by Misha Hanin

Trusted Business & Technology Advisor, Solutions Managing Director & Senior Solutions Architect at iRangers International Inc. with more than 25 years of experience in the field of information technology, infrastructure analysis and design, implementing innovative and leading technologies for International companies around the globe in public and private sectors.

Over the years I was able to develop very strong technical and engineering skills which helped me to earn trusted advisor status with our clients. As one of the nearly 500 trained Microsoft Certified Masters (MCM) in The World (during 10 years existence of MCM program, just about 500 people in The World participated in this very intensive training), I have a winning track record in building and bringing projects to operational and measurable success.

I am honored to have been awarded Microsoft Most Valuable Professional (MVP). This award is given to "exceptional, independent community leaders who share their passion, technical expertise, and real-world knowledge of Microsoft products with others."