Current setup and background

We are changing our company name. With that means changing our internal domain name, email addresses and Office 365 tenant. 100% of our mailboxes are in the cloud (Exchange online). We used to be on prem but migrated all mailboxes to the cloud. We manage users through on prem AD and ADsync them to O365. We kept the hybrid exchange server on premise because Microsoft recommends it.

The steps we are taking to accomplish this are

  1. Build a new internal domain
  2. Create 2 way trust
  3. Migrate AD objects using ADMT
  4. Build new on-prem Exchange server and populate with old domain user data
  5. Purchase new Office 365 Tenant
  6. Migrate O365 data using 3rd party tools

My question is related to step 4

Given the fact that we have no local mailboxes and everything

  • What needs to be setup on the new on-premise Exchange server to function properly in the new domain?
  • Do I need to extend the AD schema to include Exchange attributes
  • How do I populate the Exchange attributes for the users after I migrate them to the new domain (ADMT does not migrate Exchange attributes)
  • Can I bypass this all and just not have on-prem hybrid exchange?
  • Please break up your question so it's easier to read. – Andrew Schulman Mar 29 '18 at 14:25

Seeing that you're moving to a new O365 tenant I don't see that you need on premises Exchange at all. You won't need any Exchange attributes on premises. You'll manage all of your mailboxes, distribution groups, etc. in Office 365.

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  • Would I just need to manually add the email attributes that AD by default does have? ADMT doesn't migrate any sort of email attribute – Brent Mattson Mar 29 '18 at 15:09
  • You don't need any email attributes, do you? Your mailboxes will be in Exchange Online as part of your Office 365 subscription. All Exchange related attributes/components will be managed in Exchange Online. Exchange attributes only exist when Exchange exists. If those don't migrate with ADMT then you shouldn't need to do anything. Think about it this way: If this were a new domain without Exchange then you would have no Exchange attributes to begin with. Everything related to Exchange is in O365. – joeqwerty Mar 29 '18 at 15:43
  • Ok I have been testing what you suggested in our current tenant.I created a user in local AD and had it sync to O365. In order to get the @domain.com email address to show and not just the domain.onmicrosoft.com I had to manually edit the "proxyaddress" within ADSI edit. But, once I did that the user configured correctly. – Brent Mattson Mar 29 '18 at 16:45
  • It sounds like you don't have a UPN suffix configured in AD to match your verified domain in Office 365. If your verified domain in Office 365 is "example.com" then you need to have a UPN suffix of "example.com" in AD and you need to set that as the UPN suffix of your user accounts in AD. – joeqwerty Mar 29 '18 at 17:14
  • I screwed up the first time. I forgot to change the upn when I created the user. I created a new one and that fixed it. I am going to continue testing this out. Thanks a lot for the help. – Brent Mattson Mar 29 '18 at 18:06

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