Are you using Xfinity webmail or a client like Thunderbird or Mac Mail? In the client, what, if any, email address might you have set up in the "Reply To" feature? In the webmail, the only way to do this is a bit more complicated. I found this from madylarian back in 2004-----------------
"Actually, I believe you can. Go to webmail and click on "Mailbox Manager". Click on the button at the top that is labled "Add Pop Mailbox" and set your regular Comcast account there, making sure to use mail.comcast.net for the incoming mail server and your Comcast username and password. You will be able to put in any name and email address you want as the sender. That is the only way to do it in webmail.
Of course, in a real email program you can configure a "Reply-to" address that is different from the "Sender", but that is not possible in webmail."
Hopefully the information is still good. I've not tried it myself.
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