Exchange 2010 to 2013 Migration - Public folders not accessible to migrated users

This was a fun one, due to the ridiculous public folder migration process that is required to go from Exchange 2010 to 2013, you are basically forced to have the two versions coexist for a while to get everything migrated. In the interim, i ended up having to have my 2013 Client Access Server proxy all connections back to the public folder database on my 2010 server (combo Hub/CAS/Mailbox). What i noticed was that i had a few limitations and quirks:

• Users with mailboxes located on the 2013 Mailbox Server could not access public folders on the 2010 server, they received an error something along the lines of: Cannot expand the folder. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance.
• Users with mailboxes located on the 2010 Mailbox Server could not use RPC over HTTP (Outlook Anywhere) through the 2013 server.
• Users with mailboxes located on the 2013 Mailbox Server could use RPC over HTTP without a problem.
• All users could use OWA and Activesync

After quite a bit of troubleshooting, it was determined that the problem was the 2013 CAS was unable to proxy requests using RPC over HTTP to the 2010 CAS. There didn't seem to be a good reason for this, all certificates were good, internal/external URLs on all virtual directories specified properly, authentication methods configured properly, etc. Finally, this solution was found. I can't say for certain that this is the only fix required, however so far it has worked well for me.

The fix (run this on your 2010 CAS):

Set-OutlookProvider EXCH -CertPrincipalName msstd:mail.yourdomain.com
Set-OutlookProvider EXPR -CertPrincipalName msstd:mail.yourdomain.com

That's it. This is a setting that was always there on 2010 but was never needed before. Note that mail.yourdomain.com should be the CN (common name) of your certificate. You can get that, if you don't know it, by running Get-ExchangeCertificate -server 2010CAS and looking at the CN= section for the entry that has IP.WS. listed for services. The moment i did this, RPC over HTTP for all users started working, and public folder access was fixed.