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.

Note: This document explicitly does not define a protocol for "guaranteed delivery", since that term (like "security") means different things to different people. Instead, we define a more focused protocol that addresses the need for message receipts, thus solving one problem that falls under the heading of "guaranteed delivery".

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.

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.

The following business rules apply:

1. A sender SHOULD NOT include a request for message receipts when sending a message to the bare JID &LOCALBARE; of the recipient, only when sending to a full JID &LOCALFULL;.

2. A sender SHOULD NOT include a request for message receipts unless it knows (via &xep0030; or &xep0115;) that the intended recipient supports the protocol described herein or unless the use of message receipts is negotiated via &xep0155;.

3. A sender SHOULD include an 'id' attribute on the message so that the sender can properly track the receipt.

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

If a sender wishes to request message receipts, it SHOULD first determine whether the intended recipient supports message receipts. This can be done directly via Service Discovery or indirectly via Entity Capabilities.

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

Two entities MAY negotiate the use of message receipts for a given session using Stanza Session Negotiation. The parameter to be negotiated is named "urn:xmpp:receipts". Its use is illustrated in the following examples.

Although a sender MAY attempt to resend a message if it knows that the recipient supports message receipts and it does not receive a reply within some configurable timeout period, resend logic is out of scope for this specification.

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.