This case is another one of those countless issues which reminds you every day that no matter how long you have been doing migrations you can never rest on an old knowledge and experience. Rather you need to keep learning something new which may at first appear same old, that’s a nature of our job 🙂 Everyone have probably seen MAPI_E_FAILONEPROVIDER mailbox access error thousands of times and knows it may be caused by name resolution, permissions (mostly)… I have also seen some “exotic” cases where same LegacyExchangeDN was present on the proxyAddresses attribute of another recipient (Contact) preventing both Mail Sync Agent access and end user’s Outlook MAPI login. But I bet the one I am about to describe is not something you’d encounter often.
In this case my customer was a financial institution and everything was very “security tight” around this environment. I assigned “Receive-As” permission over the entire database and QMM Mail Sync agent had no problem accessing all mailboxes except this high profile VIP level person. We tried pretty much everything – removing / re-adding permissions, assigning it individually to this mailbox, trying “Full Mailbox Access” in place of Receive-As”, evaluating all the “Denies” – no luck. And then suddenly customer mentions that they run our beautiful product “Change Auditor for Exchange” (and I am not kidding here – the product is a charm and you can see here that it does work great! 🙂 ) which has “Exchange Mailbox Protection” feature enabled on this VIP mailbox. Problem solved and another new MAPI_E_FAILONEPROVIDER case goes into my “bag of migration tricks”!
[inner] System.Runtime.InteropServices.COMException: The Microsoft Exchange Server computer is not available. Either there are network problems or the Microsoft Exchange Server computer is down for maintenance. – MAPI_E_FAILONEPROVIDER (Microsoft Exchange Server Information Store) Low level error: 0x0 File: ‘aeWrapHelpers.h’ Line: ‘279’