SMTP & DNS should be run through the servers provided by the ISP for
the exact purpose. There is no valid reason for a dialup customer to
go direct to root-servers.net and there is no reason why a dialup user
should be sending mail directly to AOL, or any mail server for that
matter (besides their host ISP)
...and there is no reason for dialup customer to have direct access to
any other port either,
they´ll just use the www-proxy and other ALG services from the ISP ?