The correct option is
A Before the sender's address
Option A is the correct answer as can be understood from the
given passage. In an e-mail, the date is written before the sender's address so that the receiver knows exactly when the message was addressed to him and can also help for future reference.
Option B is incorrect because, after the sender's address, the recipient's address is given.
While writing informal emails, one may or may not include the date. But, as it's given here in the e-mail, option C is incorrect.
Since option A is the correct answer, option D, none of these, is incorrect.