Pop up in Mail Inbox

I recently noticed a new - very annoying to me - behavior when I open an email (latest version in Mail > 10.11.5):

In this particular email, someone gave me a phone number. Now, it really doesn't matter why I do not wish to add a phone number to my contact(s) - I should not have to have this pop up stare me in the face and make reading the email confusing. I have to manually dismiss it every time (and although I've done it twice already with the same email as we've been replying back and forth, it shows up again and again every time there is an update/additional reply).

I could not find how to turn this off anywhere - does anyone know of a way?