Anonymous Mail via Port 25

[nobody@shell.portal.com]

Awhile ago, someone mentioned that at some colleges & universities, the
dialup lines don't require you to log in immediately.  Rather, they let
you specify which system to telnet to, and then you log in there. 
Telnets are usually limited to machines in the University's domain, but
they often don't restrict what ports you can telnet to.  So you can
telnet to port 25 and send an anonymous mail which would be very
difficult to trace.  Does anyone know of any such systems?  Anywhere in
the U.S. or Canada?  I'm thinking of using such mail ports for a new
anonymous remailer I'm working on, and I want to make tracing the mail
as difficult as possible.  Please post modem numbers...