email browser not secure"

I have a few email accounts associated with my Xfinity account.  The address bar for the one that I use most often, right after loading my mail, looks fine.  But as soon as I click on a mail, "not secure" appears in the address bar .  It doesn't matter if the email is  of personal nature or from places that I have signed up for newsletters.  In fact, even the Xfinity news letters have this response.  How do I determine if my account is safe or not?

The only way I have found to not have that be there is to log out and back in.  But that's pointless as it will happen again as soon as I clikc on a message..

This isn't happening with the other email address that I have set up, just the one that I use every day.

Appreciate any help.