I'm currently in the process of migrating about 1,000 on-premises distribution lists (DLs) and mail contacts over to Exchange Online, and we have a hybrid setup in place. The migration plan includes several steps performed via PowerShell, such as moving all on-prem DLs to a non-synced organizational unit (OU), forcing an Azure sync, and renaming our items to avoid conflicts. My main concern is how Outlook will deal with cached addresses after this migration. For instance, if someone has sent an email to '[email protected]', but now it's renamed to '[email protected]' in on-prem and supposed to function as '[email protected]' in M365, will Outlook properly update this? I read about Outlook using the x500 address for caching, but I need clarification on that. Would simply adding the x500 address from the on-prem object to the M365 version solve this issue? Thanks!
2 Answers
You definitely need to transfer the x500 address when you migrate. Make sure you're adding the x500 address to the M365 distribution list. As for the x500 address on the on-prem side, you might want to consider renaming or deleting it to avoid any confusion in Outlook later on.
I’ve done similar migrations, and with newer Outlook versions, it shouldn't be a problem as long as user mailboxes are in Exchange Online. If you still have any mailboxes on-prem, that could lead to issues when sending emails to the native Exchange Online groups, depending on your accepted domains setup.
Good to know! We're using Microsoft 365 Outlook (classic), and all user mailboxes are in Exchange Online. So does that mean we won't need to worry about adding the x500 from the on-prem object?
It's still a concern with Exchange Classic, so stay vigilant!
Gotcha, so just add the x500 to the M365 DL. But what should I do with the old on-prem x500?