I've installed 7.0 and patched to 7.3.
I think you mean SME 7.1. Update 3, which is essentially SME 7.1.3
Do you have access to log files of the remote mail server? To me it seems that something goes wrong after a the certificate is accepted and TLS is activated and the user is logged in again:
Apr 4 01:00:01 server fetchmail[6107]: Authorization failure on chris@mail.mydomain.co.uk
Apr 4 01:00:01 server fetchmail[6107]: IMAP> A0006 LOGOUT
Apr 4 01:00:01 server fetchmail[6107]: IMAP< A0005 BAD Unimplemented command
Apr 4 01:00:01 server fetchmail[6107]: IMAP< * Logging out
Apr 4 01:00:01 server fetchmail[6107]: IMAP< A0006 OK LOGOUT completed
Apr 4 01:00:01 server fetchmail[6107]: 6.2.5 querying mail.mydomain.co.uk (protocol IMAP) at Wed 04 Apr 2007 01:00:01 AM BST: pol
l completed
Apr 4 01:00:01 server fetchmail[6107]: Query status=3 (AUTHFAIL)
Apr 4 01:00:01 server fetchmail[6107]: normal termination, status 3[/code]
What external mail server are you using? Is this an SME Server as well?
Any ideas? Does it matter that the server names are not equal?
It might be that the server name is causing the problem, why do you use server.mydomain.co.uk and not mail.mydomain.co.uk?