Microsoft Exchange 2013 CU11 slow local delivery and outbound and extremely slow external inbound messages

Hi All,

This may be a red herring as we were running sweetly for a day before this occurred.  We upgraded to CU11 on Thursday and ran ok Friday, in fact it ran better than ever.  Saturday morning users reported trouble connecting in with iPhones and reported emails not arriving from external sources.  Inbound messages from external domains (Even tiny ones of a few kb) take 3 hours to materialise into the users inbox.  Messages we send outbound take 5 mins but they were instantaneous before and local messages (Local user to local user) take 20 mins or so.

I suspected potential DNS issues and also I wondered if there was anything related to the schema or alike as it seems the Exchange Server is having trouble resolving anything.  Do we have to perform any additional functions on the Domain Controller(s).

We are not getting any NDRs.  Help please.

The server has plenty of resources and runs fine.  The disks are SSD and the Database is in a healthy state.
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purpleoakAsked:
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Vaseem MohammedCommented:
I suspected potential DNS issues and also I wondered if there was anything related to the schema or alike as it seems the Exchange Server is having trouble resolving anything.
NSlookup works fine from exchange servers?
Do you have reverse lookup PTR for all exchange servers?
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purpleoakAuthor Commented:
We found the issue to be an external dns server that was struggling to communicate with our exchange server
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purpleoakAuthor Commented:
Problem is now fixed this solution got us on the right tracks to resolve the issue completely.
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