MTOM is the W3C Message Transmission Optimization Mechanism, a method of efficiently sending binary data to and from Web services.
MTOM only optimizes element content that is in the canonical lexical representation of the xs:base64Binary data type.
Since there is no standard way to indicate whether data is in the canonical lexical representation, the mechanism for applying MTOM is implementation-dependent.
There is no guarantee that the optimization will be preserved if there are multiple SOAP nodes involved.
XOP is used as the referencing mechanism in the serialised XML infoset.