After diggin into the problem of not being able to send email, I called Comcast to learn that Comcast has turned off outgoing Port 25 on a cable modem. The user got this email message " Dear Comcast Subscriber: ACTION REQUIRED: Comcast has determined that your computer(s) have been used to send unsolicited email ("spam"), which is generally an indicator of a virus. For your own protection and that of other Comcast customers, we have taken steps to prevent further transmission of spam from your computer(s).
There are several computers and a server on the network. How can I Sniff the network and figure out which host is spamming over port 25?