I have an end referral who had a problem in that he was sending emails and they were being sent, but not being received. After much calling and asking for help, I finally got through to Martin in the CSC, and he actually led me through using telnet to send an email. This then identified that AVG was getting in the way. I'd tried disabling AVG's email applet, but I then uninstalled it completely and that fixed the problem. I must admit, I was stuck up until that point. It's so nice to see that the help is there, even though strictly speaking it wasn't PN's problem.
A friend of mine appeared to have a similar problem yesterday (different ISP). After the latest AVG update all seemed well, but neither of us were convinced the problem was with AVG as a couple of messages did get sent but there was long delays before delivery. Odd, very odd. Glad you got some useful help though.