title: Retrieve the e-mail address of a Google Form respondent without asking for their e-mail address in the form
body: <p>The scenario goes:</p>
  
  <ol>
  <li>Via email, a Google Form is sent to a respondent.</li>
  <li>Via this sent email, the respondent answers the form and sends their response. <em>This form has no email address field.</em></li>
  <li>I need to retrieve the respondents e-mail address and add it to the spreadsheet where the Google Form responses are recorded.</li>
  </ol>
  
  <p><strong>Via Google Apps script, is it possible to retrieve the respondent's e-mail address in this manner?</strong> For <em>specific reasons</em>, I am not allowed to inquire the respondent's e-mail address. Retrieving the e-mail address in this manner also serves as verification so that it is verifiable which of the e-mail addresses I sent the form to have a response.</p>
  
  <p>I am aware that if you have a field which contains the user's e-mail address, this is very do-able. There is even a <a href="https://developers.google.com/apps-script/articles/sending_emails" rel="noreferrer">tutorial</a> specifically about it. However, I haven't seen a guide for the use case described above.</p>
  
  <p>I have attempted using <code>Session.getActiveUser().getEmail()</code>. However, it seems that it only retrieves my own e-mail address (as it considers me, the person viewing the spreadsheet, as the active user).</p>