I have enabled IMAP and POP on my 2013 CAS servers. Succesfully tested access using an account with a mailbox on 2013 server. For users that have their mailbox still on 2010 server IMAP and POP don't work, and from the logfiles on the 2013 CAS server where all front end protocols are pointing, it appears that it is attempting to proxy this traffic to a 2010 mailbox server - which does not have IMAP or POP backend service (because in 2010 the IMAP and POP traffic is on the CAS server); ..;Proxy:mbx1.domain.com:993:SSL;Failed;Excpt=""A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 10.10.10.61:993-SocketException"" Is IMAP/POP supported in co-existence scenareo ? What am I missing ? Thanks.

Ran get-exchangeserver | get-imapsettings and noticed that only 1 of the 2010 mailbox servers had imap settings configured. Concluded that at one point in time this server may have had client access role as well, and uninstalling that did not remove imap4 settings. Since there is no remove-imapsettings command, I went into ADSIEdit, found and deleted the following key ; CN=IMAP4,CN=Protocols,CN=MBX1,CN=Servers,CN=Exchange Administrative Group (FYD),CN=Administrative Groups,CN=Company,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=domain,DC=com restarted IMAP4 service on the 2013 CAS server and voila... it is no longer attempting to proxy to non-existent IMAP service on my 2010 mailbox server, but is proxying succesfully to the 2010 CAS servers.