Possible Solution - Problem Could be Caused by Your Filters in Email
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I went to Comcast forums and followed suggestion there. Log onto the comcast website and go to your Mail. Go to "Settings" and then disable any filters you have under "Filter Rules". As soon as I disabled all of them, I sent myself email and it went through. The forum info stated that somehow when you try to filter out or block a particular email address, it sometimes will block everything and everyone who tries to send you mail. I don't understand it, but the solution worked in my case. I hope this might help some of you too.