You have the comcast account NOW setup in Outlook? If so the only way to get the older ones are to forward them to yourself. There are 2 protocols in mail systems. POP and IMAP. In POP systems actually download each mail message to the specific machine you are viewing them through. You will need to forward them and open them from within outlook.
Then my question to you is
Can you get into this email by comcaast website? Do you have that email going to outlook. If no. have you tried? Just trying to get more info to help understand the issue better.