Yes, they can. Comcast Security Assurance might be able to help you with this. 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.
Can any comcast email customer forward their email to my comcast email account? If they can, how can I stop it?
In addition to what Bruce said,----------------------
Assuming you are still on the old email format-------------
From your Inbox page, go to Preferences>>>>>>Email>>>>>>>>Email Filters. Click on that, and then follow the prompts to set up a filter for that sender. One of the options is "Discard", which dumps any emails from that sender and you just never see them.
If you are on the new format, click on the gear icon in the upper right corner of the screen, then on Settings. There you will see Filter Rules. Click on that and follow the prompts.
But in any event, if you are being harassed it is a violation of the Comcast ToS agreements.