How to add a reply_to in the email function

You will need to add a header to the email.

Ex. :
email( 
from: "laplante@sednove.com",  
to: "pierre.laplante@sednove.com",  
subject: "test",  
header: "Reply-To: laplante.p@gmail.com",  
message: "test" );

Url : Documentation for email function