Certainty of E-mail sent If it does not reach the recipient, it is sent back to the sender automatically. Make the sender that E-mail recipients or not to travel.
Of course, the E-mail sent to the recipient if it is returned to the sender automatically. Lets the sender know that the E-mail recipients to travel or not.
The certainty of the E-mail exported to, if not the recipient will be returned to the sender automatically, make the sender know E-mail. Travel to the receiver.