[I also left this reply to your original Discussion Item a short while ago.] Does the Activity Log have a "Email was Delivered" activity for the two that didn't receive the email? If so, then it may have gone into their Junk folder in Outlook (if that's what you are using). I have employees that this happens to periodically, so I just have them mark the email as "Not Junk", which whitelists my email address in their Outlook client and the emails don't go into their Junk folder any more.