JSONP Callback Error When send large email

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Javascript

.NET

JSONP

I have a web service to send email, when i send it small message it send successfully.
If i send a lot of date in the message it return with Fault in sending email, I try to set maxJsonLength="500000000" in web config, but still there is error.
Could you please help me in this situation.

var wsUrl = "URL";
           $.ajax({
               url: wsUrl,
               data: {

               },
               dataType: "jsonp",
               contentType: "application/json",
               success: function (json) {

               },
               error: function (e) {

               }
           });

I use this code to consume web service.