So an update the messages continued to a prospective client of mine twice the most recent one at 9:43 am this morning (its now 12:24). I talked to Comcast support which is almost like talking to a brick wall since the lady wanted me to install McAfee Security Suite on my Mac and kept calling it a PC specifically. I've stopped using Entourage and used Mail (still happens) and the ONLY thing I've noticed differently between the "rogue" emails and legit ones are the rogue one has Javamail.root@sz0147a.emeryville.ca.mail.comcast.net as the In-Reply-To. The legit ones dont have the Javamail.root portion just the random ID but everything else looks legit had the Apple Message framework v930.3 in the Mime Type, Apple Mail 2.930.3 in the X-Mailer etc etc so it looks like Mail sent it (it also tagged Entourage also).
I'm on the verge of reinstalling OSX (no archive and install) and reinstalling most of my software (there goes like 2 days at least). Running ClamXav now to see if it will pick up anything (doubtful)
reinstalling OS X or Mail or anything won't help. either through deliberate maliciousness - or through the random act of a bored script kiddie - someone is definitely putting the spoof on you. My vote is it's just randomly happening & these BS e-mails could even be 'bot behavior. I could get into all kinds of detail - but, you could just google a little bit & discover what is more probably happening to you.
Googling "mail spoofing" or "mail spoofing bot" will take you to tales of thousands & thousands of people who are going through what you are going through.
Change your e-mail addresses - notify people on your list of what's happening - and your problems should disappear.