In Hybrid, clarification of Microsoft statement "Public folders can only reside in one place, so you must decide whether your public folders will be in Exchange Online or on-premises."

Brian Hall 81 Reputation points
2023-06-27T20:26:55.9066667+00:00

I'm planning to move some small Public Folders to O365 now that we have our Hybrid environment up and working.

Several Microsoft articles I've read say the following in regards to Public Folders in Hybrid:

"Public folders can only reside in one place, so you must decide whether your public folders will be in Exchange Online or on-premises."

That is from this article:

https://learn.microsoft.com/en-us/exchange/collaboration/public-folders/configure-legacy-public-folders-for-hybrid?view=exchserver-2019

Does that mean that if I have on premise Public Folders, I can't create any Exchange Online Public Folders at all, or does it just mean that users can only access Public Folders in one location.

I do still have my Exchange 2019 Public Folders on Exchange 2019, but Exchange Online appears to have the ability for me to create a new Exchange Online Public Folder mailbox and Public Folders while the on-prem PFs still exist.

Since the PFs are small, I'd like to just export them to a PST file, create a new Public Folder Mailbox in Exchange Online, and import the PST to Exchange Online's Public Folders while the on-prem PFs still exist, and then have online users access the new Online PFs while on prem users still access the old on-prem PFs. There won't be much time until everyone is moved Online, so I'm not worried about anything being sync'd.

Can I do it this way, or will I be blocked from having any Exchange Online PFs at all while the on-prem PFs still exist?

Exchange | Hybrid management
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  1. Andy David - MVP 157.8K Reputation points MVP Volunteer Moderator
    2023-06-28T11:46:08.55+00:00

    In theory, if you were to export ALL the folders on-prem to psts and then create new PF mailboxes and their folders in Exchange Online, this would work. What you lose are permissions, rules etc... because you will need to recreate that in ExO.

    https://learn.microsoft.com/en-us/exchange/collaboration-exo/public-folders/create-public-folder-mailbox

    The restriction is that the Outlook client can only see one tree, so if you created new PFs in Exchange online, thats what the clients would see - its an all or nothing thing - they will never see the on-prem ones. The trick would be to ensure the org config is set to -PublicFoldersEnabled Local

    https://learn.microsoft.com/en-us/powershell/module/exchange/set-organizationconfig?view=exchange-ps

    Having said, Most people choose to migrate them the traditional way:

    https://learn.microsoft.com/en-us/exchange/collaboration/public-folders/migrate-to-exchange-online?view=exchserver-2019

    1 person found this answer helpful.

  2. Amit Singh 5,306 Reputation points
    2023-06-28T05:44:24.9666667+00:00

    If you connect from an external network, ensure MAPI/http is configured and published correctly. The Autodiscover process from your Exchange Online organization will "find" the on-premises public folder mailboxes you configured in the Exchange Online Set-OrganizationConfig.

    Helpful links - 

    https://learn.microsoft.com/en-us/exchange/collaboration-exo/public-folders/set-up-legacy-hybrid-public-folders

    https://community.spiceworks.com/how_to/185867-migrate-mail-enabled-public-folders-in-hybrid-mode

    Please Note: Since the web sites are not hosted by Microsoft, the links may change without notice. Microsoft does not guarantee the accuracy of this information.

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  3. Jarvis Sun-MSFT 10,231 Reputation points Microsoft External Staff
    2023-06-28T06:28:40.1533333+00:00

    Hi @Brian Hall ,

    It is not supported that an org has public folders in both Exchange Online and On-Prem at the same time.

    Even though there can be two separate PFs, Outlook can only view and access one hierarchy, so on-premises mailboxes and Exchange Online mailboxes now only see local public folders, and the migrated mailbox cannot see the organization library which hosted on Exchange online.

    You can refer to this post: https://learn.microsoft.com/en-us/answers/questions/61963/hybrid-configuration-public-folders


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