Notice-Requested-Upon-Delivery-To (NRUDT) D. J. Bernstein, firstname.lastname@example.org 19970201 1. Introduction The UNIX sendmail program has for many years supported a Return-Receipt-To (RRT) header field that requests a notice of successful final delivery. Notice-Requested-Upon-Delivery-To (NRUDT) has the same basic function. The big difference is that RRT lists the sender's address, while NRUDT lists the recipient's address. This change is critical. RRT works poorly for messages to multiple recipients, because it requests a notice from every recipient. RRT in a message to a large mailing list produces a giant, usually unintentional, flood of mail. This problem is so severe that RRT has been disabled in recent versions of sendmail. NRUDT is designed to be adopted immediately, with minimal disruption, as a solution to the problems of RRT. Note that NRUDT is merely a request for notification; unlike the link-level Delivery Status Notification SMTP extension, NRUDT does not provide a guarantee of notification. NRUDT is supported by the qreceipt program in the qmail package. 2. Syntax NRUDT is a field in the header of an RFC 822 mail message. It has the following syntax: "Notice-Requested-Upon-Delivery-To" ":" 1#address See RFC 822 for more information about header fields and addresses. NRUDT requests that, upon final delivery of the message to any of the specified addresses, the sender be notified. Note that more than one address can appear in a single NRUDT header field. Multiple NRUDT header fields should not appear in a single message. 3. Response Upon successful final delivery of a message to any address listed in an NRUDT header field, the host performing delivery may, if desired, generate a success notice. The success notice is similar to a failure notice as described in RFC 1123. Its envelope sender is <>. Its envelope recipient is the envelope sender of the original message; however, if the envelope sender of the original message is <>, a success notice is not sent. The body of the success notice does not contain a copy of the original message, but it does indicate the Message-ID of the original message, as well as the relevant recipient address. A success notice may indicate delivery to several addresses. For example, given the following message: (envelope) from email@example.com (envelope) to firstname.lastname@example.org, email@example.com Date: 1 Jan 1996 21:43:34 GMT From: "D. J. Bernstein" <firstname.lastname@example.org> Message-Id: <email@example.com> Notice-Requested-Upon-Delivery-To: God <firstname.lastname@example.org>, email@example.com (You Know Who You Are) ... a host may respond as follows: (envelope) from <> to firstname.lastname@example.org Date: 1 Jan 1996 21:43:37 GMT From: DELIVERY NOTICE SYSTEM <MAILER-DAEMON@heaven.af.mil> To: email@example.com Subject: success notice I delivered <firstname.lastname@example.org> to the following local mailboxes: email@example.com firstname.lastname@example.org Thanks for asking. However, a success notice is never merged with a failure notice.