Tracking of sent mail

Tracking of sent mail
E-mail traditionally provides no mechanism for tracking a sent message. The system(s) involved will generally make an effort to either deliver mail or return a failure notice ("bounce message"), but there is no guarantee that a message will actually be delivered, let alone read by the recipient. This is in contrast to the postal mail system, which offers registered mail or other forms of tracking and tracing.
To remedy this, the IETF introduced Delivery Status Notifications (delivery receipts) and Message Disposition Notifications (return receipts).

Return receipt

A return receipt is a postal service document confirming the arrival of a message or parcel at its intended destination. Internationally, the service is known as avis de réception (AR), but in some English-speaking countries, acknowledgement of receipt is used.

E-mail

Return receipts for E-mail are called Message Disposition Notifications (MDN). Their format and usage is outlined in RFC 3798.
A description of how multiple Mail User Agents (MUAs) should handle the generation of MDNs in an Internet Message Access Protocol (IMAP4) environment is provided in RFC 3503.
Another type of receipt is the Delivery Status Notification (DSN) receipt. The only purpose of DSN receipts is to let a sender know when the recipient's server received the message. Sender cannot be sure the message will be read but DSN is less intrusive of the recipient's privacy than MDN and nearly all servers support it.
All MUAs can receive MDNs and DSNs but not all can request them (notably: many Webmail services). Third-party tools exist to activate MDNs and DSNs in any MUA.