Hi Pranay,
I managed to send the MTOM request as a Soap through Java action using the code that I received on the forum (https://github.com/ra2085/apigee-mtom-soap/tree/master/callout/src/main/java/com/google/apigee).
Of course a lot of things needs to be done so that the message is sent from Mendix (I mean on code modifications).
Hope this will be helpful.
Kind regards,
Aleksandar Alempic