Using smtp server from ISP to send outgoing mail

So my ISP blocks port 25 for outgoing mail, now i want to use their server to send my mail.
I googled for over an hour but didn't found where i was looking for, can someone please tell me how i can send my outgoing mail through the ISP's smtp server, or maybe give a link that explains it.

I installed debian 3.1 perfect setup

 

It's explained in this post: http://www.howtoforge.com/forums/showpost.php?p=1594&postcount=18