[TO] next to email subjects?

[Kevsta26]

Ever since today, all of my emails on my iPhone Mail app have a little box that says [TO] next to the subject of the emails. What does this mean?

 

[C DM]

Sounds like you have Settings > Mail, Contacts, Calendars > Show To/Cc Label option enabled. (It's basically to indicate if the email was sent with your email address in the To field or the Cc field.)