Sincerely yours, from one of y'all
The word “sincerely yours” is an example of formal language written specifically in formal letters. It suggests that the person B.o.B is addressing to knows him already.
The phrase “from one of yours” implies that B.o.B was previously an “underdog” himself.
To help improve the meaning of these lyrics, visit “Both of Us” by B.o.B (Ft. Taylor Swift) Lyrics and leave a comment on the lyrics box