I seemed to have cracked it (it sends e-mails anyway, and YahooPops doesn't complain).
If you are using multiple SMTp servers do the same thing with the usernames, just change the port to the localhost SMTP port...bobs your mothers live in lover

So I would set my username to
thestub#localhost:25000Does that makes sence?
BTW this thread should be pinned - the info is worth keeping near the top!