In my event log,  I see the following Error, ~ ever 30 minutes:

Watson report about to be sent for process id: 38844, with parameters: E12IIS, c-RTL-AMD64, 15.00.1044.025, M.Exchange.Imap4, M.Exchange.Imap4, M.E.I.Imap4Mailbox.DetectUidCorruption, System.NullReferenceException, 3bd8, 15.00.1044.021.

It looks to me that maybe an issue with an Imap4 Client and the UID.   I've looked to either side of the message in question but I haven;t seen any indication as to which client may have the corrupted UID.

Any suggestions on how to track this error down ?

Hi,

I suggest to enable IMAP Protocol logging to review the POP3 and IMAP4 connections for troubleshooting issues.

Set-ImapSettings -Server ServerName -ProtocolLogEnabled $true

Then restart service (Microsoft Exchange IMAP4). By default, the log file path is: C:\Program Files\Microsoft\Exchange Server\V15\Logging\Imap4

If this error is related to some mailbox (Using IMAP to connect Exchange )corruption, please try to use New-MailboxRepairRequest cmdlet to repair corrupted mailbox to check this issue.

Best Regards.

You have to use the following command:

New-MailboxRepairRequest -Mailbox mailbox.name -CorruptionType ImapID - for a single mailbox
New-MailboxRepairRequest -Database database.name -CorruptionType ImapID - for a entire database