Saturday, May 28, 2016

Resolving Transport Service Pile Up related to DNS Issues

Hi folks,

Just wanted to share with you about my recent adventure. This applies to Exchange server versions 2010, 2013 and 2016. I have noticed pile up of the messages in the queues.There were thousands and thousands of them. Queues were in the Retry state with the following error:

The error was like the one below:

last error 4.4.0 DNS query failed. the error was:DNS query failed with error Error Retry

It was interesting as I had absolutely healthy DNS. Suspending and retrying queues didn't do its magic. So I went to the Event Viewer to find the following errors in the Application Log for Transport service (error 205 was followed by error 16025):

Investigation lead me to this TechNet blog post and this forum thread. The rest of the blog posts were similar to the former one. However the latter was the magic silver bullet to solve my problem.

I have checked my advanced IPv4 address configuration to discover the following:

After checking the "Register this connection's address in DNS" and restarting Microsoft Exchange Transport service on the affected server functionality of transport server. the above error disappeared and transport queues were returned into Ready and Active states with the fully restored mail flow.

Therefore, dear friends, my recommendation would be first checking DNS settings and should it not be the case then move to tweaking your transport service related DNS settings as advised by MS and other bloggers.

By the way, if anyone is curious what 00000000-0000-0000-0000-000000000000 as a NIC GUID means, it means that Exchange Transport Service is using all DNS adapters for DNS lookups.

And of course my special thanks to the author of the last comment in the forum thread. Sometimes problem can be too small and too hidden to spot it straight away and this makes the greatest fun.