Added callback after mail delivering.
Added callback after mail delivering.

Hates/spree_email_to_friend,Vakrim/spree_email_to_friend,spree-contrib/spree_email_to_friend,spree-contrib/spree_email_to_friend,Vakrim/spree_email_to_friend,spree-contrib/spree_email_to_friend,Vakrim/spree_email_to_friend,ReserveBar1/spree_email_to_friend,com123/spree_email_to_friend