a customer of us is just preparing his migration to Exchange Online. This will be done with a classic Hybrid deployment in order to use HMA. They have a lot of domains and they are all synchronized to AAD. But there are a lot of gaps regarding the mail-user creation in Exchange Online. There are users in the same domain nested in OU A and some in OU B. Users of OU A all have mail-users in Exchange Online, the others not. All OU's are synchronized.
I already checked the basics like email address filled, primary smtp matching the UPN and so on.
The user objects by the way are created in AAD, but the mail-users are missing for a lot. What else can I check to find a fix for that?
If the objects are synced to AAD but no corresponding recipient object is created in ExO, you either have some missing attribute or there's an issue with the sync between AAD and ExODS. Compare the attributes between two sample objects in both AD and the Metaverse (MIIS Client), also check for some duplicate attribute errors and such. If you cannot spot anything, open a support case as it might be an issue with the "forward sync" process.
