lammert - 1:14 pm on Jul 12, 2006 (gmt 0)

My provider allows to use their SMTP server from other networks, as long as I authenticate with my username and password which is used for their POP3 server. They haven't documented this feature very well and I discovered it merely by accident.

You could try to enable password authentication in your email program and see if your own ISP accepts SMTP connections when you are on another network. It might work.