title: Send email with default email client from a WPF app
body: <p>I am trying to find a reliable way to be able to send emails using the system default external mail client from my WPF app.</p>
  
  <p>I know similar questions are already posted on stackoverflow (<a href="https://stackoverflow.com/questions/20328598/open-default-mail-client-along-with-a-attachment">Open default mail client along with a attachment</a>), but they are outdated and I couldn't find any solution which is robust enough.</p>
  
  <p>My requirements:</p>
  
  <ul>
  <li>Works from a WPF desktop app on W10</li>
  <li>Use the external email client which is the user's default app for Email</li>
  <li>Works with the most popular email apps (Outlook, Thunderbird, 
  the Mail app in Windows)</li>
  <li>Attachments</li>
  <li>HTML, plain text and RTF body</li>
  <li>The email appears in the drafts folder and recognized as a new, unsent message by the clients</li>
  </ul>
  
  <p>The things I've found so far:</p>
  
  <ul>
  <li>mailto links: no-go because no attachment support</li>
  <li>EML file: issues like the from field has to be explicitly set and also the message is not marked as a new unsent message by some clients even if the "X-Unsent: 1" is set</li>
  <li>MAPI: Depricated by MS and they themselves do not recommend using it. People complaining about several bugs and issues. Also the default mail client is not recognized properly on Windows 10.</li>
  </ul>
  
  <p>So far MAPI seems to be the best option but honestly I don't like any of them but I couldn't find any better alternative.</p>