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Julien Schneider's avatar
Julien Schneider
Brass Contributor
Jul 12, 2018

Enable AD Connect sync with existing Office 365 accounts and mailbox

Hi,   I'm managing an Office 365 tenant with 60 users with E3 subscription. For the moment all users have a username with @mydomain.onmicrosoft.com domain and a mailbox associated.   Now, I want ...
exchange
hybrid
office 365
Nestori Syynimaa's avatar
Nestori Syynimaa
MVP
Jul 24, 2018

Hi Julien,

 

It doesn't matter what the UPN is, as long as it matches the user's login name. Or are you saying that your on-premises UPN is not an email address, i.e. username@domain.local? If so, when configuring Azure AD connect, just select to use mail attribute for UPN and you should be fine.

 

You do not need Exchange to convert users to shared mailboxes, you can do that in Office 365 too. Last time I installed an Exchange server from scratch, it took 10 hours or so. How difficult it is, depends on your current environment etc.

dan_jjjj's avatar
dan_jjjj
Copper Contributor
Aug 11, 2020

When I try this, I get an AttributeValueMustBeUnique error when it tries to syncronize for the new user since the UserPrincipalName is not unique. I followed the guide on this page...

https://support.microsoft.com/en-us/help/2641663/use-smtp-matching-to-match-on-premises-user-accounts-to-office-365

 

Do you know how to get around this?

 

p.s. Sorry for posting on an old thread. It was one of only a few that I could find that directly discusses AD Connect to an existing 365 company. 

 

Thanks

 

 

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