1. Go to Office 365 Admin.
  2. In navigation on the left select the Exchange admin center from the list of admin centers.
  3. Go to the Mail Flow navigation item on the left
  4. Go to the message trace navigation item at the top
  5. Enter your search criteria in the presented form
  6. Click search and see results.

Keep in mind that the results show times in UTC by default. So dont let this throw you off thinking it is your local time.