Some external Users are getting Duplicate Emails from our domain. I have Exchange 2013 and is properly configured. A user reported me that, I sent one email to the other domain's user, and it was delivered twice after 1 or 2 hours. I checked the Message track log on exchange servers and email was resubmitted and sent from the edge server after 2 hours.
I have no idea why this is happening? can you please help me on this issue.