Problem with migrating IMAP mailboxes to Exchange Online.

[kkrasuski]

Hello, I have a problem with migrating IMAP mailboxes to Exchange Online.

I created several migration tasks via "Migration Batch" but most of them fail because some of the mails e.g. 10 out of 1000 cannot be migrated properly. The error in each case is the same. Example of error

Data migrated: 1.874 GB (2,012,587,176 bytes)
Migration rate:
Error: TooManyTransientFailureRetriesPermanentException/DataConsistencyTransientException: Error: The job encountered too many transient failures (61) and is quitting. The most common failure is DataConsistencyTransientException with the hit count 59. --> The data consistency score (Investigate) for this request is too low (due to LargeItem).

At first I thought that the source mail server has emails over 35MB and exceeds the default message limit, but after increasing the limit in EXO the problem still occurs. The migration report generated by EXO also does not say much except that in the "DataConsistencyScoringFactors" column next to the mailboxes with failed migration there is a value : LargeItem

I also cannot perform the "approval" operation because EXO returns an error:
SkippedItemApprovalTime: Parameter 'ApproveSkippedItems' is not available for users of type 'IMAP' - the property is not relevant to users of this type.

Has anyone already encountered this problem and is able to help me?

[#2]

No one replied because there is no way to fix this. You can start the migration batch or use SyncNow and it will sync again, and go through one good sync, but it will just say Failed again. So you basically have to switch your MX records and give it enough time and then do one final sync and when done delete the batch.