You
are assigned a port at smtp.smtpport.com which then forwards
all data to port 25 of your mail server.
For
example, you sign up your server, mail.yourdomain.com. After
signing up you are assigned a random port number 23287. You set your
mail client to connect to smtp.smtpport.com on port 23287
and are now able to send and receieve e-mail normally despite your
ISP's block.
<E-mail Client Configuration Instructions>