All unread emails are marked as NEW in the list of results.
To mark an email as read, find that specific email in the Communications tab's search results, and click on the three dots at the end of the line. The dropdown menu will open:
Click on Read option to mark the email as read. That email will not be marked as NEW anymore.
To mark multiple emails as read, first, select them using checkboxes:
And after that, click Mark as read button: