In older Xfinity email, I customized how long I could "sit" on an email in my INBOX list before it was automatically marked as READ. I had it set to about 4 seconds. In the new email, the moment I highlight an email in the list, it is marked as READ, even though I haven't opened it.
Especially a problem when I delete one email and th e system jumps to the next email in the list, marking it as READ.
How to fix?
What you are describing is the default behavior in the new email format. If you want to select a message in the list without opening it, click on the checkbox to the left of it.