The More Instant Messaging Interoperability (MIMI) working group will specify
the minimal set of mechanisms required to make modern Internet messaging
services interoperable. Over time, messaging services have achieved widespread
use, their feature sets have broadened, and their adoption of end-to-end
encryption (E2EE) has grown, but the lack of interoperability between these
services continues to create a suboptimal user experience. The standards
produced by the MIMI working group will allow for E2EE messaging services for
both consumer and enterprise to interoperate without undermining the security
guarantees that they provide. The working group will aim to achieve the
strongest usable security and privacy properties for each targeted functional
Recognizing the need for a standardized security protocol to support group key
establishment, authentication, and confidentiality services for messaging, the
IETF has specified the Messaging Layer Security (MLS) protocol
[I-D.ietf-mls-protocol] and architecture [I-D.ietf-mls-architecture]. MLS is
agnostic to the identity system used within any given messaging service; it
provides confidentiality of sessions once the participants in a conversation
have been identified. To achieve interoperable messaging, the MIMI working
group will specify how one or more identity building block technologies (for
example, X.509 certificates or Verifiable Credentials) can be used to establish
end-to-end cryptographic identity across messaging services, assuming the use
of MLS for key establishment.
Interoperable messaging in federated environments requires consensus on a
common delivery service and a transport protocol between federated domains.
Specifically, the MLS protocol requires ordering of handshake messages within
groups to ensure clients can synchronize despite asynchronous message delivery.
This working group will specify a flexible solution for transport and delivery
that takes into account typical requirements and best practices from the
Achieving interoperable messaging among MIMI-compliant services requires a
solution for the introduction problem, i.e., the ability for a user in one
application to take an identity of a target user along with the associated
application, be granted permission to initiate communications, and be able to
establish communications with the target. The working group will specify a
solution to the introduction problem, together with best practice
recommendations for functionality, configuration options, and other aspects.
The working group may also choose to specify a solution to discover the set of
preferred messaging services associated with a given identity. Express and
implied user preferences about discoverability and reachability must be
Modern messaging services commonly support numerous features including plain
and rich text, delivery notifications, read receipts, replies, reactions,
presence, and many more. The working group will identify an extensible baseline
set of messaging features and specify a content format to allow this feature
set to be implemented interoperably. This format must be usable in the presence
of E2EE. In defining the format, the working group will seek to reuse existing
primitives (especially existing semantics) including previously defined message
headers, MIME types, and URIs where practical.
In its initial phase, the working group will focus on solutions for messaging.
The working group will aim for general-purpose designs fit for both 1:1 and
multiparty messaging. The working group will not standardize new audio/video
signaling or media protocols but may recommend the use of existing protocols
and suites such as SIP and WebRTC.
The following are out of scope for the working group:
* Metadata processing to manage spam and abuse
* Interoperable mechanisms for group administration or moderation across systems
* Extensions to the MLS protocol. If needed, requirements will be referred to
the MLS working group or other relevant working groups in the security area.
* Definition of completely new identity formats or protocols.
* Extensions to SIP, SDP, MSRP, or WebRTC.
* Development of anti-spam or anti-abuse algorithms.
* Oracle or look-up services that reveal the list of messaging services
associated with a given user identity without the user's permission.
Numerous prior attempts have been made to address messaging interoperability,
including the IETF's extensive prior work on XMPP, SIP/SIMPLE, and their
related messaging formats. The MIMI working group will draw lessons from these
prior attempts, seek to avoid re-hashing old debates, and will focus on the
minimal standards suite necessary to facilitate interoperability given the
feature set of modern messaging applications.
MIMI will communicate with related working groups as needed, including MLS,
STIR, OAUTH, GNAP, and the W3C Verifiable Credentials WG.