On-prem Public Folder access for migrated O365 mailboxes

Matt Pollock 246 Reputation points


I recently migrated a test mailbox from Exchange 2019 on-prem to Office 365 (Hybrid setup already in place)

I followed the steps in this guide to allow on prem public folder access to the migrated user.


Everything looks OK as per the guide.

The O365 user can see the "Public Folders" menu item in Outlook, however when I expand the PF I get an authentication prompt.

The user creds don't work, the prompt comes back.

This behaviour is as per the note in the guidance:


I don't understand why the migrated user cannot access the public folder structure.

The user AD account is still in scope of the AADConnect sync
The mailbox has a public folder mailbox assigned

Can anyone shed any light on this please?


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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Exchange Server Management
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Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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  1. Matt Pollock 246 Reputation points

    Picking this issue back up after a couple of months, still struggling with it.....

    The issue:

    Mailboxes migrated from on-prem (exch 2019) to O365 cannot access on-prem public folders once migrated.
    The public folders menu item exists in Outlook, but the O365 mailbox user receives a repeated credential prompt when trying to expand the folders.
    The steps outlined in this documentation have been followed:


    One prerequisite of the documentation however states that:

    ****"An Exchange Online, Microsoft 365, or Office 365 user must be represented by a MailUser object in the Exchange on-premises environment in order to access Exchange Server public folders. This MailUser object must also be local to the target Exchange Server public folder hierarchy."****

    This cannot be correct however, as any migrated mailboxes whereby the associated account still exists as an on prem AD account will be represented by a "RemoteMailbox" object in Exchange on-pre rather than a "MailUser".

    Not sure if this is the root cause of my issues but I could use some clarification if possible.


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