Same comments than issue #4473:
- you might split your patch into smaller patches
- Do you really need to keep a reference to the "raw" socket?
- I don't understand what is sock.shutdown(SHUT_RDWR). When is it 
needed? Does it change the behaviour?

Oh, another comment:
- When I fixed poplib/imaplib in py3k, I created a _create_socket() 
method which to factorize the "classic" class and the SSL class. The 
classic class uses socket.create_connection() which supports IPv4 and 
IPv6 (and maybe other protocols) whereas the SSL version reimplements 
create_connection(): "for ... in getaddrinfo...". So you may reuse 
this idea for in your SSL refactoring (for POP3 and IMAP4).