Migrate Distribution List from On-Prem to Office 365

Joel Rocha 21 Reputation points
2023-01-06T15:14:02.867+00:00

Hi everyone!
I know there's a looooottttt of cases like this and I read them all! :) and none of them made it clear for me!
I am making a migration from on prem to Office 365. Nowaday we are in hybrid environment. We have all mailboxes already on 365 and working fine, and now I need to migrate the distribution lists.
My doubt is: I know I'll have to recreate every DL on the 365 side, but I am having troubles with that once I can not create a DL on 365 side without erase the original at the onprem side. I am not allowed to do it because when I try to create on 365 it says "The email address is already being used by an active ‎group‎", which is the group on onprem, which I can see on the 365 side.
Do I have to delete the DL on on prem so that I can create them on 365 side? We have millions of DL, I am really afraid of doing that and them something gets wrong and we stay without DLs neither in on prem as on the office 365 side!
Can someone share these little first steps on how to do it?
Thank you so much for your attention!

Microsoft Exchange Online
Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Andy David - MVP 144.4K Reputation points MVP
    2023-01-06T15:17:20.693+00:00

    you have to either mail-disable the group on-prem, delete it completely or change the on-prem Email Address to something not in use first.
    Once it syncs to Azure, you can then create a new group with the old SMTP addresses of the group.

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  1. Jame Xu-MSFT 4,171 Reputation points
    2023-01-09T08:25:34.563+00:00

    Hi @Joel Rocha ,
    You have to remove the distribution list from their on-premises environment and recreate it in Office 365.
    If you have not read this case, you may refer to: Exchange migration to O365 - Should you migrate all DLs/Contacts?

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