We recently helped an organization to convert their Microsoft Exchange environment to run in Hybrid mode. The goal was to move all of their email users to Exchange Online (Office365), then decommission their on-prem Exchange environment once everyone had been migrated. We used the latest version of DirSync (now called Azure AD Connect) so users would be able to authenticate to Office 365 services (through Azure AD) using their internal AD credentials.
As our team began migrating a group of pilot users to Exchange Online mailboxes, we found that once a user had be migrated they were unable to email some of the internal users (about 25 out of the 3000 users) which had not yet been migrated.
Unfortunately, our Microsoft partner had no clue how to resolve the issue and we opened several cases with Microsoft wasting many hours of time with no good results.
Our Microsoft partner eventually said we would need to remove those 25 users from DirSync and then re-add them which would mean 25 users would need to take all their documents out of OneDrive and then put them back in, plus they’d have to re-setup their Teams groups and re-follow every document in SharePoint Online they had previously followed. Essentially it meant a huge pain for those 25 users which included 2 executives, as well as several senior managers and remote sales staff. This would result in a terrible user experience and a ton of work and we weren’t confident it would even resolve the problem.
Thankfully, we eventually figured out a much better solution:
- Go to Office365 admin portal and assign an Exchange Online license to any user who cannot be emailed by another user that already is using Exchange Online. Note: generally this would be a BAD idea idea because now the user has both an on-prem mailbox and an online mailbox and they would need to check both mailboxes in order to receive all their email.
- Wait ~30 minutes for replication within Exchange Online
- Ensure a DirSync (Azure AD Connect) synchronization has run in the last 30 minutes. if it hasn’t, run it manually.
- Remove the Exchange Online license for the user. This should delete the Exchange Online Mailbox so the user has only their on-prem mailbox again. and remove the BAD situation with two mailboxes (which the user should never have known you did)
- Wait ~30 minutes for replication within Exchange Online
- Ensure a DirSync (Azure AD Connect) synchronization has run in the last 30 minutes. if it hasn’t, run it manually.
This procedure resolved our email flow issues for every user that was having problems.
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