While &xep0079; provides message acknowledgements at the server level, it does not extend that model all the way to the client. However, sometimes client-level acknowledgements are needed, for example to provide "receipts". This document defines a mechanism for XMPP message receipts, which are functionally equivalent to the "delivered" or "displayed" event in &xep0022;, which this specification in part obsoletes. This specification does not distinguish between delivery and presentation, as was done in the message events protocol, in part because no existing clients make the distinction.

Note: This extension is functionally equivalent to an Advanced Message Processing rule of "receipt" but uses a dedicated namespace to simplify processing by end user clients and intermediate routers.

This document addresses the following requirements:

1. Enable a sender to request notification that an XMPP message stanza has been received.
2. Enable a recipient to provide message receipts if desired.

This document defines a protocol that enables a sender to ask the recipient to return a receipt for a message. Although the return of a message receipt lets the sender know that the message has been delivered, there are many reasons why the sender might not receive a receipt immediately or at all, including but not limited to the following:

• The sender addressed the message to the recipient's bare JID &LOCALBARE; and therefore does not know if the recipient even supports message receipts.
• The sender has not bothered to determine whether the recipient supports message receipts.
• The recipient (or the particular intended resource to which the sender addressed the message) does not in fact support message receipts.
• The intended resource supports message receipts but the recipient's server delivers the message to another resource that does not support message receipts.
• The recipient's client receives the message but experiences a malfunction before generating a receipt.
• The recipient returns a receipt but the receipt is lost on the way back from the recipient to the sender (e.g., because of connectivity issues or software failures at any hop).

As a result, this document does not define a protocol for complete reliability or guaranteed delivery, and those who implement and deploy this protocol need to be aware of its limitations, as described throughout this specification.

Note: Message receipts can be combined with the rules specified in Advanced Message Processing (e.g., the deliver rule) for more complete reporting.

If an entity supports message receipts, it MUST report that by including a &xep0030; feature of "urn:xmpp:receipts" in response to disco#info requests:

Support can also be determined via &xep0115; a.k.a. "caps".

A sender could request receipts on any non-error message (chat, groupchat, headline, or normal) no matter if the recipient's address is a bare JID &LOCALBARE; or a full JID &LOCALFULL;. Whether it is appropriate or advisable to do so it another question. This section provides recommendations about when and when not to request receipts, and what results to expect in each scenario.

In order to make it possible for senders to request and for recipients to generate message receipts, we define a dedicated protocol extension qualified by the 'urn:xmpp:receipts' namespace.

There are two allowable elements in this namespace:

• <request/> -- included by a sending entity that wishes to know if the message has been received.
• <received/> -- included by a receiving entity that wishes to inform the sending entity that the message has been received.

Specifically, the receiving entity shall return a <received/> notice if it has received and processed the message. The term "processed" is understood to include presentation to a human user if appropriate or any other application-specific client-side processing, including generation of an error response if the application determines that the message contents cannot be handled.

The following is an example of a message that includes a request for return receipt.

Note: A sender MUST include an 'id' attribute on every message that requests a receipt, so that the sender can properly track the receipt.

The recipient shall generate a receipt if and only if it supports the protocol defined herein and it is configured to return receipts, either globally or for this recipient (otherwise it MUST NOT return a receipt and SHOULD NOT return an error).

The <received/> element SHOULD be the only child of the &MESSAGE; stanza and MUST mirror the 'id' of the sent message.

It is possible for a recipient to leak its presence when returning message receipts; therefore, a recipient SHOULD NOT return message receipts to senders who are not otherwise authorized to view its presence.

No interaction with &IANA; is necessary as a result of this document.

Thanks to Joe Kemp and Kevin Smith for their input.