To remove a contact's access to a message that was already sent to multiple contacts, follow these steps:

  1. In your application, go to the Messages tab;
  2. Select "View Sent" and open the message in question;
  3. Go to the Recipient List and delete the desired Contact from that list.

 

If you want to delete the message completely after it has been sent, removing access to all recipients:

  1. In your application, go to the Messages tab;
  2. Select "View Sent", and select and delete the message in question.

 

In any of the above cases, your contacts will still have the link to your message but, if they open the link, they will be warned that the message is no longer available.