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.