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Title
mailbox migration fails. Exception of type 'Quest.Rest.RestException' was thrown.; WebStatus = Success; StatusCode = ServiceUnavailable; StatusDescription = 'Service Temporarily Unavailable'; Content = '{"message": "Service is temporary unavailable"}' -
Description
During the migration of just one user's mailbox we get:Exception of type 'Quest.Rest.RestException' was thrown.; WebStatus = Success; StatusCode = ServiceUnavailable; StatusDescription = 'Service Temporarily Unavailable'; Content = '{"message": "Service is temporary unavailable"}'There's also other log entries indicating MS throttling, such as:"Waiting for Microsoft Azure to send the response back, The server cannot service this request right now. Try again later. waiting 0.01 minutes before resuming.This particular mailbox, in both migration attempts, the Microsoft throttling occurred and then the next event to happen was the error and "Failed to migrate mail". And then the task stops.We had already already relaxed EWS Throttling before the migration. [Though even with the EWS throttling relaxed, MS throttling can still occur, just not as often / strictly as without it having been relaxed.]There are other migration workloads (not mail migrations) occurring simultaneously. -
Cause
That indicates the throttling occurred and then for some reason the migration task stopped before completion instead of waiting for the throttling period to run its course. There's suppose to be a 'Migration Summary' log entry end the end of a mail migration task this log doesn't have that entry. The event logs end abruptly.There are other migration workloads (not mail migrations) occurring simultaneously. At the same time there was OneDrive Assessment task running as well. It may have been this task that caused the throttling in the mail migration task Unlike the mailbox EWS throttling, the MS throttling for other workloads (OneDrive, Teams, etc.) cannot be loosened. -
Resolution
Migrate the mailbox again when there are no other mail migration tasks running nor migration tasks running in any other ODM workloads (eg. OneDrive, Teams, etc.) .