For POP and IMAP access to Exchange Server mailboxes the best practice is to require secure logins.
Don't Leave POP/IMAP Protocol Logging Enabled
Why I recommend you don’t leave POP and IMAP protocol logging enabled on Exchange Servers.
Exchange 2010 FAQ: Can I Access Public Folders Using IMAP?
In Exchange Server 2003 it is possible to connect to public folders using an IMAP4 connection. Is this still possible with Exchange Server 2010?