Hi Shujaath,
Thanks for the reply.
If you create a new account in local AD, can this UPN been synced to Office 365?
Do you mean the existing accounts (onmicrosoft.com) can’t been synced to domain.com for login to the portal?
Please tell us how do you do the Dirsync and which kind of accounts you want to sync.
To find the root cause of the issue, could you please also give us the screenshot of the problem account’s UPN setting via private message?
To see the private message, please perform the following steps:
1. Please go to "Your details" section on the right side of the community site.
2. Click Private messages.
3. Click the subject title of the response to read the message.
4. Provide a screenshot of the issue like the following screenshot:
Image may be NSFW.
Clik here to view.
Thanks,
Jason Jiang