Exchange 2010 and "Multiple MAPI public folder trees were found" error

A customer in an Exchange 2010 environment was giving the error "Multiple MAPI public folder trees were found" on both IPM_SUBTREE and NON_IPM_SUBTREE. This error is commonly reported as being a problem with multiple instances of "CN=Public Folders" under the Public Folder Hierarchy key in ADSI Edit. This was not my problem, however i will list both solutions. Note that i did not need to restart my Information Store service(s) for this to start working again, but not all environments are the same.

Open ADSI Edit

This needs to be done on a machine with adsiedit.msc, usually a domain controller will work fine. After opening it, you need to connect to the Configuration context. Once connected, drill down to Configuration, Services, Microsoft Exchange, <Your organization name, typically Microsoft Exchange>

Solution 1

Continue drilling down into Administrative Groups, <Your administrative group name, typically Exchange Administrative Group>, Folder Hierarchies

Once here, you should see an entry for CN=Public Folders. If you see more than one, there is one that either needs to be deleted, or you need to edit the attributes and set msExchPFTreeType to 0 (this is slightly safer).

Solution 2

If solution 1 didn't work, this may be your problem. As it turns out for this customer they had an Exchange 2000 environment a long time ago that they "had a hard time removing". With those comforting words, i looked elsewhere and found this.

Still in adsiedit.msc, but in the Microsoft Exchange key, look for a CN=Public Folders entry. Chances are this is the one that you need to delete or set msExchPFTreeType to 0. You cannot just rename the object, it will still be detected as a msExchPFTree type.