Ah, I think I know what it is...
Do to anti spam measures, ISPs secure their SMTP so that they will only relay SMTP traffic into or originating from their own network.
All outgoing mail will need to go through the SMTP server of your host provider, wether you receive POP email from any provider. This is just a simple config to point all your email clients to the exact same SMTP server, the one that is provided by your ISP.
Another possible problem is that your ISP is using ESMTP. This is an enhanced version of SMTP and has a few extra functions. Your email client may not understand some of the commands.
Can you ping smtp.onetel.com?
Can you config your outgoing email to point to perdition2.onetel.com?
Email me off list and I will send you a piece of software that you can insert between your email client and server. This will tell us if comms is actually working. (Do the obvious to my email address)
Regards, Dave.