Once you Comcast account is closed, you need to move your files quickly, as at anytime, Comcast can stop access to your old account/email. It could be days or weeks. No way of knowing.
If you already have a new email address somewhere else, you could forward them all from Smartzone. If you do that though, they emails will show as having come from YOU, not the original recipient.
IF you also used andd will continue, to use an email client (Outlook, Windows Mail,etc.) you can set up rules in the email client to move the emails to it.
In addition, you could send all email to a free account, such as Gmail.
Once you tell us what you use, we could assist you further.
Need Email Help? Please post the following information in your post. Do you use XfinityConnect? The Full or Lite version? Do you use an email client? Which one? (Eg; Windows Live mail, Outlook, a smartphone etc.) Which browser/version do you use? And- have you cleared your browser cache? Which operating system? XP, Vista, Windows 7, Mac OS X Details of the problem you are having.