If you do socket.setdefaulttimeout(X) before trying to
instantiate imaplib.IMAP4_SSL(), the connection hangs
partway through the SSL negotiation.

The cause is that socket.ssl() is actually incompatible
with timeouts (not sure why) and IMAP4_SSL() doesn't do
anything to guard against it.  It should do
.setblocking(1) on the socket.socket object before
passing it to socket.ssl().

The documentation should also clarify timeouts not
working with socket.ssl.