title: Multipart forms from C# client
body: <p>I am trying to fill a form in a php application from a C# client (Outlook addin). I used Fiddler to see the original request from within the php application and the form is transmitted as a multipart/form. Unfortunately .Net does not come with native support for this type of forms (WebClient has only a method for uploading a file).
  Does anybody know a library or has some code to achieve this? I want to post different values and additionally (but only sometimes) a file.</p>
  
  <p>Thanks for your help,
  Sebastian</p>