Is there a way to mark xinity emails as READ?

The link:   https://connect.xfinity.com/faq/email.html#markReadUnread shows several ways to mark an email as Unread.  Even though the link title shows   .........#markReadUnread I am unable to find any mention in the article about how to mark an email as  "READ".  Am I missing something in the article, or is there a separate article that shows how to mark an email as READ?

I open emails and sometimes do not have the time to completely read the email or some time later ( a couple of days or 2-3 weeks)  want to revisit a particular email that I have read.  The read email are still present in the inbox, but there is no way (that I can find) to list only the email that have been read or opened.  It would be a big help to be able to mark emails as READ or opened and be able to show a list, in date order, of emails that have been read or opened; and then select an email, from the list, to be opened.

This would be very similar to the "search" box, in the upper left corner of the email inbox view.   You can type a word or phrase in the search box, press return, and a list of emails, from the inbox, that contains the search word or phrase is presented.  Actually, the search box can be applied to what ever folder is present, inbox, sent, trash, .... or All..

Seems like it would be relatively easy to be able to mark emails  "READ" (presently, they can be marked as Unread) and then have a special, unique, word or phrase to enter in the search box (to avoid confusion with intentionally searching for the word "read") which would return a list of all email that have been marked as read and then select an email from the list.

Comment or suggestions welcome.