[nuclear500]

[ QUOTE ]
Comcast is blocking your port 25 to any SMTP servers except their own. You can either change your Exchange server to listen on an alternate/additional port (587 is common), or use their SMTP server (smtp.comcast.net) to send mail.

Large ISPs do this as a preventative measure against comprimised computers sending out large amounts of spam.

[/ QUOTE ]

You cannot use Outlook from a remote location to connect to an internal corporate Exchange environment over the Internet unless you are using RPC over HTTPS. This means absolutely all communication with Exchange, and therefore sending emails, is occuring over port 443 and 80 to his companies Exchange front-end servers.