OK so I checked and we do have a reverse DNS entry set up for our IP address. Just a moment ago, a order confirmation bounce came in from comcast although we have setup the SPF record and the reverse DNS entry. Maybe it takes a day or so but I will keep you posted regarding what happens.

Lastly I also filled out the form to request to be removed from comcasts black list at: Blocked Provider Request Form
so I hope this helps too and according to what I've read it should.

Thanks everyone.