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How do I enable Office 365 users to access legacy on-premises Public Folders?




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    Matthew B


    Good information. Question from my side, I migrated my PF's from on-prem to O365, however for the life of me I can not get mail-enabled PF's to receive email.

    I have done all the steps of set the domain in O365 tenant to Internal Relay, set he mail-enabled PF's to allow anyone to send to them and removed the requirement to authenticate. Internal users can email the PF's fine, but an external user it fails with an NDR every time, as if the on-prem does not know where to send the email. The MX records point to the on-prem still.

    Any thoughts?

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    Rob Latino

    Hi Matthew B.

    I've asked one of our technical SMEs to respond here. You should hear back shortly.

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    Rob Latino

    Hi Matthew B.,

    Sorry for the delayed response. One of our technical SMEs look at your message and provided the following response:


    Some assumptions about how the environment is configured:

    1. It's a hybrid deployment.
    2. All users were moved to Office 365.
    3. Public folders were moved to Office 365 and the Office 365 access was changed as per this KB, which provides a different set of instructions than the above KB.
    4. When users email a public folder from an internal email it works.
    5. When users email a public folder from an external email it generates an NDR.

    You should test this:

    1. Does it work if the users email from an on premises mailbox to an Office 365 public folder?
    2. Does the address users are trying to email matche or is a valid smtp associated to the folder?
    3. Is there any mail enabled object on premises, with the same address of the public folder, that will forward the email to Office 365 when it hits the on premises server?

    Ideally MX records should at this point be pointing to Office 365 but if they are not, then testing 1 above will help us validate if the problem is in the Exchange on premises (our guess is that it is), 2 will help make sure users are trying to email the correct address and in case 1 doesn’t work, then 3 is the solution. If there’s no object in the Exchange on premises email will never get to Office 365. Either you change the MX or you create mail contacts for all public folders.


    Overall, there are a lot of variables in this scenario that need to be confirmed. Your best option if none of the above works is to contact support at

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