Something that has occurred to me.
Has he installed any antivirus or firewall software recently? One of these could be blocking the sending of any mail.
I am pretty sure that you are way off track with the port no but if you want to change it then go into OE - Tools - Accounts - Mail tab - Choose the account - properties - advanced here you can change it. The reason I think this is not the problem is that is is impossible to put 0 in this box.
Try another web based mail account than Hotmail / Yahoo as they are both really crap at the moment. Try setting up an account with a mobile phone co or similar.