Migrating shared mailboxes to Office 365 is one of those things that is starting to become easier over time, especially with full access permissions now working cross premises.
One little discovery that I thought I would share is that if you have an Exchange 2010 hybrid configuration, the auto mapping feature will not work cross premises. (Exchange 2013 and above, you are ok and have nothing to worry about).
This means if an on-premises user has access to a shared mailbox that you migrate to Office 365, it will disappear from their Outlook even though they still have full access.
Unless you migrate the shared mailbox and user at the same time, the only option is to manually add the shared mailbox back into Outlook.
Something to keep in mind especially if your user base accesses multiple shared mailboxes at a time.

Exchange, Office 365
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Join the conversation! 2 Comments

  1. Thanks for posting this. Have encountered the same and verified not an issue in a separate Exchange 2013 hybrid environment. Interested to know you thoughts on why it doesn’t work with Exchange 2010 though; Do you think it’s the missing functionality of OAuth which can’t be enabled with a Exchange 2010/Exchange Online hybrid?

    • Yeah I have a few different theories, OAuth being one of them. I know EX2010 struggles to understand the receive connectors created by a EX2013 or above hybrid server due to the new features introduced. So missing functionality is a sticking point.
      I also went down the path of manually updated users msExchDelegateListLink AD attribute with the DN of the shared mailbox to force auto mapping during the autodiscover process. This didn’t work so could be something related to autodiscover in EX2010.

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