I would favour point (1). This is what i communicated to the users already. It's simple and fits the overall problem the best. There is many cases where a) you dont know the exact mimetype b) data is send inlined c) you need to pass the content type along DataHandler is the best chioce IMO. Regarding Noel's considerations: anonymous wrote : | I see base64Binary data that should not be considered as attachment. It's a type that is often used for IDs. For exemple, you can have an operation with an ID as argument and an attachment as a result. | It's right what you are saying, but in the only (rare) case this becomes a problem is when users types contain base64 types that should be optimized and others that shouldnt at the same time. If this doesnt occur on the same payload then you easily turn off MTOM for that port. On the otherhand, if you want to meet that rare case a treshold switch should be used to decide at runtime wether or not optimization should be done. This is a good idea in many cases, because MTOM optimization does pay off only when data reaches several kb. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4004817#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...