. The default address for all emails sent by your blog is currently wordpress@ yoursite.com.
I had seen some tutorials / forum entries previously where people suggested editing the core WordPress file 'pluggable.php' to overide this default. This method does work, however you would have to repeat the hack every time you upgrade to a new version of WordPress so it is not an ideal solution.
Faced with this problem you can use the excellent pluging :
SB Welcome Email Editor
vous pouvez personnaliser le mail de notif d'inscritption et le mail de l'expediteur de votre choix