Return-Receipt-To

A sender can request a return-receipt by including this header field. The return-receipt is sent to the Return-Path address of the email and not to the address specified in the Return-Receipt-To header field. This header is non-standard and mostly not supported. Use Disposition-Notification-To instead. Even if supported, there is no guarantee of a receipt being sent.

Example:

Return-Receipt-To: recipient@chilkatsoft.com