Simon, your explanation sounds plausible, as the Belize connection (I am not in BZ) was the only reason I could figure out as to why comcast users wouldn't receive my email, even though I could get theirs.
SJ - you may want to check to make sure others who have emailed you aren't waiting for a response (because you didn't get the message).
I had to use a different email address (on the same computer) to get through to comcast users, who requested through Comcast to allow me through. Email to them seems to work ok now.
Scuba - former Insight users in Spfld are not happy with the change either