The last few days I've had the problem that external e-mails are not received by our users. I've restarted the server and that solved the problem for a day, but now we experience the same problem. Internal e-mails are sent and received without problems and also sending to external addresses works fine. I've used the Exchange Remote Connectivity Analyser and it gives the following error: The server returned status code 451 - Error in processing. The server response was: 4.3.5 Server configuration problem This server has been running without problems for almost a year. What can the problem be?

and what happens to those emails? Do they boucne back to the sender? If so, what is the exact NDR? Everything look good here:? http://www.mxtoolbox.com/

and what happens to those emails? Do they boucne back to the sender? If so, what is the exact NDR? Everything look good here:? http://www.mxtoolbox.com/

HI Oliver, What is your setup structure (HUB,CAS,MXS) and EDGE) and how you have configured internal email flow for inbound. Do you see any major event log in event in HUB server. What about if you manually test mail from external source thru SMTP command. Anil

Ok, problem is solved. Seemed that 3 Gb of free space on the C: partition was just below the threshold of the Exchange Transport... I shrunk the 50 Gb pagefile to 10 Gb ! (48 Gb ram in this server)