Making Modern Public Folder Migration Easier


We are making it easier to move your existing public folders to Exchange Online modern Public Folders. We are introducing 2 improvements to make this migration easier – first we have increased the size of public folder mailboxes from 25 GB to 50 GB – increasing the standard storage size for modern Public Folders in Exchange Online to approximately 2.5 TB. We are also making it possible for Exchange Server 2003 customers to utilize an Exchange Server 2010 Hybrid to enable Public Folder migration to Exchange Online. These updates help remove challenges in migrating your existing public folders to Exchange Online. Let’s have a look at the benefits and impacts of these changes.

Increasing Exchange Online Public Folder Mailbox Size

The larger public folder mailbox size provides you the ability to store a larger amount of data in modern public folders. Each tenant provides 50 public folder mailboxes now with a 50 GB quota – thus Exchange Online provides approximately 2.5 terabytes of public folder data in the cloud. This removes challenges we have seen in some migrations where the total volume of data exceeded the prior 1.25 TB limit.

The increase in mailbox size does not increase the size of a single public folder. We continue to recommend that you limit the size of any single public folder to 15 GB prior to migration. This recommendation is two-fold – it provides the best service experience and it avoids situations where public folder splits are required at migration. This limit is truly for a single folder – it does not include child folders for the calculation of a folder size. You should review the size of your current public folders prior to migration and reduce the size by deleting or separating large single public folders to ensure the best public folder experience in the service.

As the service is enhanced with changes, you should remember you still have control as the service administrator. You retain the control to reduce the public folder mailbox quota – however you are prevented from configuring quotas values larger than 50 GB in the service.

In the Exchange Online public folder mailbox quota is managed for you – the system monitors and automatically triggers public folder splits to best utilize use public folder mailboxes in the service. Splits are managed by the service and are transparent to users and service administrators. The end result of a split process is to keep all public folder mailboxes within the service limits.

Migrating Exchange Server 2003 Public Folders

This change helps customers migrating from Exchange Server 2003 to Exchange Online – as we have previously noted you can’t directly migrate Exchange Server 2003 Public Folders to Exchange Online. Now you can obtain and use the Exchange Server 2010 SP3 Hybrid to host your existing public folders on the hybrid server for purposes of migration. This migration to Exchange Online requires you move your existing public folder replicas to the hybrid server so there are no replicas left on Exchange 2003. We make multiple hybrid server keys available to you to retain public folder high availability on-premises during your co-existence phase. The scope of use for the Exchange 2010 Hybrid server in this case is limited to temporarily hosting on-premises Exchange Public Folders, solely for the purpose of migrating such Public Folders to Exchange Online. You can request a hybrid server key from Office 365 support.

What’s Next for Public Folders

We are working to provide additional control in the provisioning of public folders. In the future we will extend the New-PublicFolder command to specify an existing or new public folder mailbox, thus enabling admins to control the destination of public folders and avoid situations where a split process is required soon after migration. This is extremely useful when performing PST based public folder migrations.

Learn More About Public Folders

For complete details about Public Folder migration read the TechNet Article for Public Folders in Exchange Online.

Special thanks to the entire Public Folder Feature Crew and Brian Day for contributing to and validating this data.

Brian Shiers

Comments (13)
  1. Peter Morgan says:

    What exactly is new in the Exchange server 2003 public folder migration process? I though the process was to always migrate to exchange 2010 and then to exchange online…

  2. Hmmm says:

    And, of course, once again the EAC interface users get the shaft. Why not just drop EAC completely and just offer po-shell interface? Writing windows-based interfaces for windows-based applications appears to be a dead art form.

  3. @Hmmm, a graphical interface for PF migrations is something the team is investigating but can make no guarantees on at this time. It is a unique scenario because it is a one-and-done migration where a UI would only be used one time. There is somewhat of a precedent for this kind of situation if you look back at LDAP to OPATH updates for Address Lists, GALs, and EAPs.

  4. Petri X says:

    How about cross forest migration for the Public Folders. Is it still no can do directly from E2003 –> E2013?

  5. KarlBystrak says:

    Can you give us some idea when you will make Public folders that contain calendars available in OWA?  I have customers who are demanding this every day.   If exchange is no longer going to include an Outlook license with each CAL then you need to make OWA a fuller featured client.  

  6. Nino Bilic says:

    @KarlBystrak – while we can't give you dates at this time, we are definitely aware of this limitation and that our customers want this functionality. Thanks for your feedback (I'll forward this on to the relevant team also).

  7. Kanika Ramji [MSFT] says:

    @Petri X – public folder team is working on enabling support from E2010 and E2007. The path to migrate from E2003 will require a hop via E2010 to get to E2013 public folders.

  8. elliotg@unimelb.edu.au says:

    In have a question about public folders and Exchange online on an issue which is not actually referenced in this article. We are currently planning a gradual migration from our on-premise Exchange 2010 installation to Office 365. This will involve a fairly
    long Hybrid stage during which our migrated users will require access to the on-premise PFs.  I have read

    technet.microsoft.com/…/dn249373%28v=exchg.150%29.aspx
    and this seems to be achievable. However, one question troubles me.  All our on-premise mailbox servers, including those with PF replicas are on a private network and are not visible from the internet.
     Hence even when we add the CAS role to these servers, Exchange Online will not be able to get directly to them. We will also be installing a couple of Exchange 2013 coexistence servers into our on-premise environment. Will this be enough to allow PF access,
    or will we also need to publish the mailbox servers via something like TMG?

  9. elliotg@unimelb.edu.au says:

    We would be really grateful for an answer to the question I posted.  We cannot be the only site with mailbox servers that are not visible from the internet. We have tried raising this question through our Premier Support agreement, but the answer we got back was not very clear. We have reached the point where we might have to postpone our move to Office 365 due to this uncertainty over what we need to do to make Public folders work for migrated users. This would not be a good look.

  10. @Elliot, you need Outlook Anywhere for your legacy environment enabled, configured, and reachable for hybrid PFs with the legacy PFs on-premises to work. This means you'll need to publish at least some CAS to the internet so OA connections can be made.

  11. elliotg@unimelb.edu.au says:

    Thanks Brian.  This is good news for us.  We already have Outlook Anywhere enabled, and in use, for our legacy environment, so this should give us no problems!

  12. jung@roschmann.de says:

    Still working on Migration ex2007 to ex2013… when will be CU3 released?

  13. Rajeev Ujjwal says:

    Brian and Team,

    As per my view, there was no migration tool to migrate the Exchange 2003 Public Folder to Exchange 2007/2010 in cross forest environment. Only the MS tool i have used IOREPL to replicate the data and export the permission and set into Exchange 2007/2010 by ExFolder. Could you please provide more views on PF migration from Exchange 2003 to Exchange 2013 or is it first need to go Exchange 2010 and then to Exchange 2013.

    Please note that i am not considering any third party tool/scripting solution in above scenario.

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