What must be included with the affidavit when serving by mail?

When serving documents by mail, it is essential to include the signed return receipt confirming receipt of the documents. This signed receipt serves as proof that the recipient has actually received the mailed documents, which is critical in legal procedures where notification of service is required. The return receipt acts as a formal acknowledgment of delivery, ensuring compliance with legal standards for service of process.

Without this signed return receipt, there would be no verifiable way to confirm that the documents were delivered to the intended recipient, potentially jeopardizing the legal proceedings. Therefore, including the return receipt is a fundamental aspect of serving by mail, making it the correct choice in this scenario.