Can I display the user who commented email?

Can I display the user who commented email?
using the

 global $user;
print_r($user->mail); 

it displayed the current user email , what i wanted is to display the email of the user who commented.

hmnbm
Submitted by nada123456 on Mon, 11/02/2009 - 11:48.
nada123@hotmail.com

nada123@hotmail.com is the current user email while nada123456@hotmail.com is the email of the user called nada123456 who posted the comment.

any help please