Now someone at Comcast tells me that I could have filtered all e-mail that did not visibly list my address. Unfortunately, he didn't know how to do it himself.
True, the spam I was getting never showed my comcast.net address. It was addressed simply to one address I never heard of, with my address, and undoubtedly zillions of others, hidden ("blind").
I searched through Outlook's filtering stuff but couldn't find anything. Can anyone shed light on this?