Does anyone know if this error message indicates the message is not entering our gateway due to MTU size? Or is it something else? Please give any information you are aware of. With many thanks, Coquette4 451 Backend Replied 4.7.0 Timeout waiting for clien I will continue trying to send the message until it is delivered

You're not receiving all external email? Do some eventually come in but is delayed? Where did you get this NDR message? Does exchange receiving internet mail directly or you have a gateway smtp server? Seems like you are greylisting\throttling\tarpitting them, or possibly a firewall\proxy is preventing bdat chunking. Check your smtp logs. James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

Thank you. Will do.