Remove Header and footer from the response which is a multipart response with file and content

Hi All,

we are currently working on the integration where we are sending a document and payload using multi-part form data to another system and we are retrieving the document back on request basis into Appian via Integration object using REST API Calls as we cannot keep the documents in APPIAN. 

Document can be any MIME-Type, In this case, we are taking example of .msg file format. when we retrieve the document back from other system, they are attaching boundary data & MIME Type details as shown in the below screenshot. Because of this, .msg file is unable to open after we retrieve the document into Appian and downloaded. Only way is to remove those line items from the document as marked and resaved it.

can someone suggest here anyway to ignore the line items in the response and able to open the file.

Here is the response

Here is the way that I setup my Integration object