title: How to set multiple DeliveryNotificationOptions for a single MailMessage?
body: <p>I want to send notifications on:</p>
  
  <ul>
  <li>Success</li>
  <li>Failure</li>
  <li>Delay</li>
  </ul>
  
  <p>when I send my emails.</p>
  
  <p>Unfortunately, it seems like the <a href="https://msdn.microsoft.com/en-us/library/system.net.mail.deliverynotificationoptions(v=vs.110).aspx" rel="nofollow noreferrer">DeliveryNotificationOptions</a> enumeration doesn't include an option to do all of these:</p>
  
  <pre><code>+---------------+----------------------------------------------------+
  | Member Name   | Description                                        |
  +---------------+----------------------------------------------------+
  | Delay         | Notify if the delivery is delayed.                 |
  +---------------+----------------------------------------------------+
  | Never         | A notification should not be generated under       |
  |               | any circumstances.                                 |
  +---------------+----------------------------------------------------+
  | None          | No notification information will be sent. The mail |
  |               | server will utilize its configured behavior to     |
  |               | determine whether it should generate a delivery    |
  |               | notification.                                      |
  +---------------+----------------------------------------------------+
  | OnFailure     | Notify if the delivery is unsuccessful.            |
  +---------------+----------------------------------------------------+
  | OnSuccess     | Notify if the delivery is successful               |
  +---------------+----------------------------------------------------+
  </code></pre>
  
  <p>I'm not able to set more than 1 options like this:</p>
  
  <pre><code> Msg.DeliveryNotificationOptions += DeliveryNotificationOptions.Delay;
  </code></pre>
  
  <p>What other options are there?</p>
  
  <p>The best that I can think of would be to extend MailMessage with an IEnumerable of DeliveryNotificationOptions but I'm not quite sure how I'd use it.</p>
  
  <p>Is this a viable way of doing this?</p>