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Insufficient system resources – Exchange Server 2007 Transport 452 4.3.1

Published on August 21, 2013 by in server

Link:  https://support.appriver.com/KB/a449/insufficient-system-resources-exchange-server-2007.aspx

Insufficient system resources – Exchange Server 2007 Transport 452 4.3.1


My end users aren’t receiving any inbound mail and when I check Delivery Queue, the following message is displayed in my mail:

“return-path address <johndoe@sender.com> rejected by mail.mydomain.com:25 : 452 4.3.1 Insufficient system resources”

To correct this issue, you need over 4 GB of free space on the volume where the Queue database is located.

Specific Details

Within your MSExchangeTransport, you will find an Application Event Log. The Event Properties Description dialog box will display the following message “The resource pressure is constant at High. Statistics… “. The description will also state that inbound mail submission has stopped, and it’s due to disk space being low on the volume where the queue database is located.

                  Image:  Event ID logged by MSExchangeTransport 

What is Back Pressure?

In Exchange Server 2007, the transport service monitors system resources such as disk space and memory on the transport servers (the Hub transport and Edge transport servers), and stops message submission if it is running low on these resources. It continues to deliver existing messages in the queue. When resource utilization returns to normal, it resumes message submission. The feature is called Back Pressure.

Changes to Back Pressure Settings in Exchange Server 2007 SP1

The Back Pressure settings in Exchange Server 2007 RTM stop inbound mailflow if free disk space is below 4 GB. This static threshold has been lowered in SP1 to a more realistic 500 MB.


Note: Configuration options for transport servers are saved in the XML file,EdgeTransport.exe.config, which is located in the following directory (\Exchange Server\Bin\).

To free up some space on this volume, you may move the Queue database over to another volume with ample free space by following this procedure. Note that this is documented in “How to Change the Location of the Queue Database”.

  1. Add the following key in the <AppSettings> section in EdgeTransport.exe.config:<add key=”QueueDatabasePath” value=”D:\Queue\QueueDB” />
  2. Restart the MSExchangeTransport service, and then the message submission will resume.Note: The Back Pressure feature, which detects resource pressure on Exchange Server 2007 transport servers and stops accepting new message submission if low on resources, may be turned OFF by following these steps. Please note that this procedure has not been recommended by Microsoft.
  3. Using Notepad, open the EdgeTransport.exe.config file from \Exchange Server\bin directory.
  4. Add the following key+value pair:<add key=”EnableResourceMonitoring” value=”false” />
  5. Save the file.
  6. Restart the Microsoft Exchange Transport Service (MSExchangeTransport).


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