Server-side function to generate and send an email with encrypted attachment content.

sendEmail.gs

function sendEmail(cipherText, recipients, userMessage) {

  // Get email address of file owner and assign attachment title.
  var fileOwner = Session.getActiveUser().getEmail();
  var fileName = DocumentApp.getActiveDocument().getName() + ".pdf.tdf3.html";
  
  // Provide a basic email body for recipients who do not support HTML.
  var emailBody = fileOwner + " has shared the encrypted file " + fileName + 
      " with you.\r\n\r\nIt\'s attached below; please download to open in" + 
      " Virtru\'s Secure Reader.";
  
  // Assign values to variables in emailHTML.html template.
  var htmlContent = HtmlService.createTemplateFromFile('emailHTML');
  htmlContent.fileOwner = fileOwner;
  htmlContent.fileName = fileName;
  htmlContent.userMessage = userMessage;
  
  // Create subject line based on filename and owner email address. 
  var subject = fileOwner + ' has shared a secure file: "' + fileName + '"';
  
  // Convert ciphertext string to HTML blob.
  var blob = Utilities.newBlob(cipherText, 'text/html', fileName);
  
  // Send the email with the tdf.html blob as attachment.
  MailApp.sendEmail(recipients, subject, emailBody, {
    name: fileOwner,
    attachments: [blob],
    htmlBody: htmlContent.evaluate().getContent()
  });
}