IBM and Microsoft have published MTOM Serialization Policy Assertion (WS-MTOMPolicy) Version 1.0.

This specification describes a domain-specific policy assertion that indicates endpoint support of the optimized MIME multipart/related serialization of SOAP messages defined in section 3 of the SOAP Message Transmission Optimization Mechanism specification. This policy assertion can be specified within a policy alternative as defined in WS-Policy Framework and attached to a WSDL description as defined in WS-PolicyAttachment.