Is the issue still occuring? Are these emails you'd like to receive or are they spam? Spammers sometimes create messages that look pretty similar, but they're not. Another way to check would be to login to the Xfinity Connect webmail site and use that to see how many instances of the messages are there before you use your Outlook Express.
Have you checked to make sure that XfinityConnect is not set to forward email? To check:
In XfinityConnect, click on Preferences, then click onj EMAIL on the left side. A window will open: Go down to the blue link titlede 'Auto Forward' and click on it. See if there are any addresses set up for forwarding. If they are, remove them, and click on OK.
Also do check your Settings in Outlook Express too. Do you have OE set up under the Advanced tab to 'Leave a copy of messages on the server'? (Comcast XC Inbox) when downloading to OE?
NOTE: The bad news is also that Microsoft is no longer supporting Outlook Express. That means no more updates, security updates,etc. It is time to switch to a new email client. I would recommend setting up and configuring Windows Live Mail. Do read the information in this link:
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.