How do I stop duplicate email from xfinity@updates.xfinity.com?

I get duplicate copies of every email message from xfinity@updates.xfinity.com. For each legitimate email, I will receive 8-12 or so duplicates over the next day or two. Every message has the same timestamp, even when it is delivered the next day. They are identical. I have contacted my ISP and they can't explain it. The mail messages are not stuck in the mail queue and being resent, for example. I have not been able to solve this while chatting with Xfinity support.

If anyone has a way to stop email from updates.xfinity.com I would do that, but I think one cannot unsubscribe from them.

Thank you for your help.