can't stop forwarding e-mail

my wife has a working comcast e-mail account. however, anyone who sends her an e-mail gets a automated reply from yahoo that says "delivery to recipients aborted". her yahoo account is not active, and any attempt to log-in sends me into a circular run-around. somewhere in the process of setting up her e-mail my adult son managed to "forward" her comcast e-mail to her now inactive yahoo account. we use windows live mail and I checked under message rules and there is nothing being forwarded that way. I also logged into her e-mail through the comcast website and there is nothing being forwarded that way. everyone who sends her an e-mail thinks she isn't receiving any e-mail but she is. HELP!!!