Precedence: P.S or Address?

In an e-mail similar to this, where is it correct to add a post script?

Before or after the signature?

Dear Professor X,

I am John Smith....

​Sincerely yours, ​

John Smith

P.S. Position 1

VLSI Design Lab
Department of Computer Engineering
X University of Technology 11155-11365

P.S. Position 2