Hello,
What you need is access to an SMTP server that will allow you to send messages from any network.
ISPs often block access to their SMTP servers from outside their own network, which is probably what you're experiencing when you're away from home.
Probably the easiest way to get access to an SMTP server and keep your existing email address is to open a Gmail account. Then you can use Google's SMTP server (smtp.gmail.com) from anywhere as long as you authenticate yourself with your Gmail user name and password first. Your email client will handle this for you once you've set it up.
If you need any help setting up your email client to use Google's SMTP server, just let me know which email program you're using and I'll see if I can find a tutorial somewhere.
-peviha