I have one employee who uses Mac mail client on his laptop connected to our exchange server 2003.
When he sends an email to a group, 3 recipients(two domains) receive duplicate emails every 10 minutes or similar interval. I checked Queue in Exchange server, the email bounded to the two persons were stuck and shows as 'Active' and '28 times failed'. But the recipients say they already received the same email multiple times.
Right now, I froze the outgoing email in queue so I can take a look at it more. I'm not sure if this is their domain email server problem or our email server or the Mac mail client. There seems some mail exchange communication problem between any of three.
To troubleshoot, what should I look at?