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Hypercat (Deb)Flag for United States of America

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Cutover v. Hybrid Exchange migration

I'm preparing to do a migration from an on-prem Exchange 2019 server to Microsoft 365.  I've read a number of articles regarding how to do both a Hybrid and Cutover migration.  The firm has only 20 mailboxes but between active and archive mail databases, there is about 600GB of email to be migrated.  I would prefer to do a Hybrid migration because it seems less disruptive to the users.  

HOWEVER, I want to end up in a situation where there is no on-premises Exchange server, so I'll be uninstalling Exchange from the on-premises server at the end of the process.  The articles I'm reading insist that if you're using "directory synchronization" then you have to leave the on-prem server up and running.  I'm completely stymied by this reasoning.  We already have a Microsoft 365 tenant set up for the firm with Azure AD synch running.  It's working perfectly fine. All the user accounts are synched and they've all been licensed for Office 365.

So, my question is: Are they referring to a different "directory synchronization" method (i.e., ADFS) that requires Exchange to be running?  If not, how would doing a Hybrid migration and then uninstalling the on-prem Exchange server break or cause issues with Azure AD?


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Avatar of DEMAN-BARCELO (MVP) Thierry
DEMAN-BARCELO (MVP) Thierry
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Thanks, Thierry. I'm not sure I follow you exactly in terms of the schema attributes.  In terms of the user accounts in AD, the only attribute I know of that relates to Exchange is the proxyAddresses.  In the past when I did a GMail to O365 migration, I had to add the email addresses manually to this attribute.  Once they were added, everything worked perfectly through Azure AD Sync.  Would uninstalling Exchange on-prem remove these attributes from the user accounts in the on-premises Active Directory?
@Saif Shaikh:  OK, you confirmed my thoughts about the proxyAddresses attribute, except my last question about whether the uninstall of Exchange would actually remove them.  Sounds like the answer is "no."  Could you confirm?

Thanks!
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I have no problem with having to do manual editing in AD. The likelihood of having to change anything is very slim and, as I said, there are only 20 users so it's not that much of a chore.

Thanks to both of you for your helpful answers.

Deb
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