Mailbox Migration Error

Royal D Costa 241 Reputation points
2021-05-10T08:40:11.51+00:00

Hi All

i have a environment in which there are 2 forests AD and exchange servers, all users from both Exchanges will be migrated to Single tenant. both Exchange servers all together have more than 250 domains. right now i am facing following Challenges in creating/migrating users/mailboxes.

**Conditions - All users must be in On premises AD and mailboxes in Exchange Online **

Problem 1 - every domain has info@keyman .com email ID s, so all together we have 200 Info Id s alone, as a rule of thumb there cannot be same UPN in the Azure AD. so migration doesn't happen.

Problem 2 - for some email Id s i deleted On prem AD account and mailbox and created new new AD account on prem and allowed it to sync. after the synchronization i noticed that new user is created as info3453@keyman .onmicrosoft.com instead of info@keyman .com .

can someone help me to understand how exactly this works and how to migrate all mailboxes smoothly under this condition.

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  1. KyleXu-MSFT 26,196 Reputation points
    2021-05-11T06:48:30.917+00:00

    @Royal D Costa

    First, one AAD could sync multiple forests: Topologies for Azure AD Connect

    If you want to keep those mailboxes using original email address(such @domain1.com, @domain2.com, @domain3.com), you need to add those domain name into Office 365. Otherwise, those mailboxes will use Exchange online default domain name(@keyman .onmicrosoft.com).

    So, it will not an issue that each domain has a info mailbox, if they using different domain name.


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