Exchange Server ports, plural; there are MANY ports which must be open on
both Comcast and whatever firewall this Exchange Server sits behind.  It is,
therefore, highly unlikely that you were making a direct connection with
this Exchange Server via Comcast unless you either created a VPN tunnel into
your corporate network, or you had Outlook 2003 configured to do RPC over
HTTP:

http://support.microsoft.com/kb/829134/en-us
Support WebCast: Using Microsoft Exchange over the Internet (RPC/HTTP) with
Microsoft Office Outlook 2003

You could also have been using POP3 or IMAP4 instead of the native Exchange
Server mode; these would use either port 110 or 143 (which usually are not
blocked by ISPs).  If so,  post back and we'll go into more detail.

Hal