I created an Exchange Online mailbox but it doesn't appear in on-prem EAC. How do I fix?

Iron Contributor

I discovered this issue because the CRM for Outlook add-in (the modern one, not the full client) complained that a new user was not logging in with the same email address and is Dynamics 365.


I couldn't confirm this no matter where I looked so I checked his Office 365 user and, sure enough, his default SMTP address is rather than


I also notice that he doesn't have any of the other standard aliases that other users have.


The key difference with him is that he's the first new user I created where I didn't first make an on-prem mailbox and migrate it up. Not knowing any better, I thought, "Why go through that step? I'll just create the mailbox in the cloud."



At this point I'm a bit unsure what step to take next. When I look at EAC on-prem I don't see his user there at all. All other users either have a mailbox type of "User" or "Office 365".


Should I migrate him to on-prem then back?

11 Replies
You need to "master" the mailbox in on-prem, the migrate it to O365 for the on-prem EAC to see it and for the mailbox to pick up your recipient policies.

What do you mean by "master"? Migrate it to on-prem?

Delete it and create a new one on-prem, then migrate *that* one to O365.

Uh oh... what about the mail that's already in it? There's not much but I'll need to preserve it. I've never needed to it before but can I export to PST and then import into the new box?

Yeah I'd do that. You can always use MigrationWiz to migrate from mailbox to mailbox, but if there's not much in there then just use the PST method.

I have no solution for the issue you described other than save the email to a pst, delete the mailbox and recreate it but there is another way to proceed other than create it on prem then migrate it.


This is how I do it for new users.


I have an exchange 2013 CAS server in hybrid mode. This is where my Exchange Admin Center is.


Login to the EAC. By default the EAC will show Enterprise settings as opposed to Office 365.


Click recipients then mailboxes. You should see all your users.


Click the + sign then select Office 365 mailbox.


This action will create the user in AD and most importantly that user will show up in the EAC. Wait a little bit and you will see the newly created user on your domain controller as well as in the O365 Admin center. You will then have to assign a license to the user and the rest is as usual. There will be no need to migrate from on prem to online.

Try these commands on your on-premise exchange management shell


Enable-MailUser -Identity <email address> –ExternalEmailAddress < email address>

Enable-RemoteMailbox <username>


@Lorenzo Moore  This is exactly what I was looking for thank you!

also works for me! thank you very much!
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