I'm facing an issue where shared mailboxes in Microsoft 365 are not auto-mapping in our Outlook desktop apps. We migrated to Exchange Online last year and completely decommissioned our on-premises Exchange server. Our active directory (AD) users sync to 365 from our old server. I normally create shared mailboxes by setting up a local AD user, syncing it, assigning a license to create a mailbox, converting it to a shared mailbox, and then unassigning the license. Although I can map and unmap shared mailboxes created before the migration, the new ones aren't showing up. I've checked the autodiscover settings, and the shared mailboxes appear correctly under the XML output. I've also tried modifying the msExchDelegateListLink attribute, but it didn't help. A Microsoft representative mentioned that I may need an on-premises Exchange server and suggested running a command to grant permissions for mapping. I'm wondering if that's correct or if there's something else I'm missing.
4 Answers
If you haven't already, you might want to use the command 'Enable-RemoteMailbox' to set the mailbox properly. Make sure to run it through the Exchange Management tools, though I believe you need at least Exchange 2019 CU12 for that.
Have you checked that AutoMapping is enabled on the mailbox permissions? It's supposed to be true by default, but there's no direct way to verify it. You can see the shared mailboxes under alternative mailboxes if they are mapping correctly.
Just out of curiosity, which operating system are you running? I’ve heard that Outlook for MacOS has issues with auto-mapping shared mailboxes, but I haven’t encountered that problem on Windows.
It sounds like you're dealing with a common issue. Just a heads up: shared mailboxes only auto-map when individual users are set as delegates. If you're using groups for access instead, they won't auto-map in Outlook, but users can still add the mailbox manually or access it through OWA.
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