The prober is, sadly, too much of an optimist.  We need to check that UIDL and TOP work here.  I wish I could be an optimist too and have us deal with this when we actually break/see such a POP3 server, but the fact that partners are indicating they only have POP3 available in this day and age also suggests they may have sucky POP3 servers available in this day and age to boot.

Suggest doing "UIDL 1" and looking for an +OK.  If we get an -ERR, possibly because the mailbox is somehow empty, we then follow up with just "UIDL".  If we still get an -ERR we can conclude the server sucks and refuse to use it.  If UIDL worked on "UIDL 1", we issue "TOP 1 0" and take an +OK as success.  If UIDL claimed there were no messages we give the server the benefit of the doubt because I fear QA will test with empty folders and file bugs if we fail to create an account in that case.

In the event UIDL or TOP fail, we return a new error code which we shall document in mailapi.js as 'pop-server-not-great'.  I was thinking 'pop-server-sucks', but we do surface the error code to the UI and that is perhaps a bit rude.  This will need to propagate to your gaia patch too.  I suggest an error string like "Server Unsupported. The POP3 server does not implement required features."

We need a canned test for this to go in test_incoming_prober.js.