Forwarding mail to another server

[Pat Maddox]

My ISP (Bresnan) blocks outgoing traffic on port 25.  I'd like to make
it so that the mail program automatically forwards requests to my
ISP's mail server, instead of trying to directly send mail to the
appropriate server.

For example, if I did
mail pergesu at gmail.com

And sent a message, my machine would send that to mail.bresnan.net and
have them pass it on.  Is it possible to do that?  If so, how?

Thanks, Pat