The "Email Safe List" won't help when a message is blocked or filtered as spam. Comcast does not offer a way for customers to "unspam" an email address themselves, but their Security Assurance group might be able to fix this for you. Give them a call at 1-888-565-4329 (from http://constantguard.comcast.net/help/report-abuse/). Note that this is NOT one of the general customer service numbers.
The first-line reps there are sometimes not very helpful. If so, be persistent, and keep at them until you get a satisfactory answer.
Without their help you can't do anything about email they block, and the only thing you can do to prevent email from going to the spam folder is to turn off spam filtering completely so that everything they deliver is placed in the Inbox.