During my day to day work as a part of support organization, I work with and help troubleshoot mailbox migrations very often. One type of migrations that we see quite often is IMAP migrations. I want...
Updated Nov 21, 2023
Version 5.0
Blog Post
Mirela_Buru
Microsoft
MicrosoftDo you mean the Incremental Sync won't complete or Initial sync won't complete in an IMAP migration?
When the IMAP migration users are Synced (initial sync is done), you would change the MX record to point to the cloud and emails will be getting delivered to the cloud mailbox. As long as you have a sync request going (get-syncrequest -mailbox <user>), this will sync every 24h the newest emails (incremental sync) and you can check last successful sync timestamp on the sync request and the cloud mailbox contents to see if changes are synced. You would delete the batch when all emails are getting delivered to O365 mailboxes and there are no more recent emails that should be synced to cloud during incremental sync (typically 72h after you changed MX, as per https://docs.microsoft.com/en-gb/office365/enterprise/powershell/use-powershell-to-perform-an-imap-migration-to-office-365?redirectedfrom=MSDN#step-5-route-your-email-to-office-365
When the IMAP migration users are Synced (initial sync is done), you would change the MX record to point to the cloud and emails will be getting delivered to the cloud mailbox. As long as you have a sync request going (get-syncrequest -mailbox <user>), this will sync every 24h the newest emails (incremental sync) and you can check last successful sync timestamp on the sync request and the cloud mailbox contents to see if changes are synced. You would delete the batch when all emails are getting delivered to O365 mailboxes and there are no more recent emails that should be synced to cloud during incremental sync (typically 72h after you changed MX, as per https://docs.microsoft.com/en-gb/office365/enterprise/powershell/use-powershell-to-perform-an-imap-migration-to-office-365?redirectedfrom=MSDN#step-5-route-your-email-to-office-365
So, if incremental sync won't complete, you will be missing in cloud mailbox the newest emails that are in the onprem mailbox.
If initial sync won't complete, then this could be entire onprem mailbox content missing from cloud mailbox.
If initial sync won't complete, then this could be entire onprem mailbox content missing from cloud mailbox.
Regarding Outlook clients, this depends on the primary smtp address domain that they should be configured on. That domain must point to autodiscover.outlook.com (cloud) for the cloud mailboxes so that Outlook can discover that the mailbox is hosted in O365.