Get Thread Original Source
This endpoint returns thread source as a message/rfc822 response.
Request
GET /v2/conversations/123/threads/456/original-source HTTP/1.1
Authorization: Bearer oauth_token
Accept: message/rfc822
Response
HTTP/1.1 200 OK
Set-Cookie: JSESSIONID=FEB3E27BFD80046C0B4954209FB79628; Path=/; HttpOnly
Content-Type: message/rfc822
thread source text
thread source text