Adding user mailbox's hybrid exchange

Hi all, I am relatively new to exchange and have inherited a Hybrid Exchange 2013 / Office 365 setup. With staff members on local exchange and students on 365. I have created a several new users in AD but can’t figure out how to add mailbox’s for them. The company that did the original setup left no documentation and I hit a pay wall when I tired asking them for any information. I would really like to know if this can be done via the PowerShell exchange management console or if I could use dir sync to automate the creation in any way depending on OU.
The setup
1 x Local Exchange 2013 server holding all staff mailboxes
1 x ADFS server
1 x ADFS proxy server
Current Domain:
Office 365 Domain:
All current staff email extension (and a few on 365):
All Student (365) email extensions:
All new students I wish to add are in a unique OU in AD, when I launch the Exchange ECP I have an enterprise and office 365 option at the top of the page. Under enterprise I can add a new mailbox but not under 365. When I go to add a new mailbox in Enterprise I can see the option for 365 mailbox but I can see a way to link it to an existing user I don’t know what I am missing but it’s all confusing as. Thanks in advance
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Vasil Michev (MVP)Commented:
If the user is synced to O365 *and* does not have a on-prem mailbox, all you need to do is apply an Exchange Online license to him via the O365 Admin portal -> Users -> Active users. Or the corresponding PowerShell cmdlet Set-MsolUserLicense.
Dead_EyesAuthor Commented:
Thanks for the quick response Vasil but I don't seem to have a Users-> Active users option in my 365 portal (see attached). How do I check if the user is being synced?
Vasil Michev (MVP)Commented:
That's not the O365 portal. is what I mean.
Dead_EyesAuthor Commented:
Thanks that's given me a load more options including activation. I will test first thing tomorrow but I am sure that was it. Do you know if this can be done with PowerShell as it took me the best part of 30-40 mins to make my way though that list?
Vasil Michev (MVP)Commented:
You can follow the instructions here:

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