We have an outside client that is having trouble getting emails through to our company's domain. According to him, when he sends a message he get's the following NDR:
"Could not deliver the message in the time limit specified. Please retry or contact your administrator.
<DM2PR02MB365.namprd02.prod.outlook.com #4.4.7 smtp;550 4.4.7 QUEUE.Expired; message expired>"
I'm stumped as to where to even begin? Any direction would be greatly appreciated!