Having Trouble Receiving Emails from Office 365 to Exchange Server 2003

I was having trouble receiving emails from Office 365 on my Exchange Server 2003 lately. It seems that any email sent from Office 365 got bounced back after 2 days of trying with diagnostic information attached like below: 9/11/2015 2:27:25 PM – Remote Server at domain.com┬áreturned ‘550 4.4.7 QUEUE.Expired; message expired’ 9/11/2015 2:07:22 PM – Remote Server at domain.com┬áreturned ‘451 […]