[Exim] smart host

Trying to setup a smart host since my isp blocks port 25 for smtp.
Do I add the following lines to /etc/exim.conf?

     internet:
       driver = domainlist
       transport = remote_smtp
       route_list = * mail.isp.net bydns_a

I would replace "mail.isp.net" with my isp "mail.mindspring.com", but
whats bydns_a and what should I set it to?