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How to troubleshoot “Insufficient system resources” errors on Exchange

Written by Abderrahim Ibnou El Kadi on . Posted in Best Practices

Symptom: Your email gateway server is unable to deliver messages to your backend Exchange mail server because of an “Insufficient system resources” error.

Source: This is an Exchange-specific issue, which happens when less than 4 gigs of free disk space remain on the Exchange server’s queue drive for a particular domain.

Here’s a sample log snippet from our own gateway server:

“Delivery of message E:\SPOOL3\DOMAINS\FN.CL\B0055738340.RCP to recipient  is delayed: ‘452 4.3.1 Insufficient system resources\r\n’.Message E:\SPOOL3\DOMAINS\\B0055738340.RCP deferred (.DEF) for recipient(s) in domain“


Analysis: This is likely caused by the back pressure feature in Exchange’s Transport Service. In Exchange Server 2007, the Transport Service monitors system resources such as disk space and memory on the Transport servers (e.g., Hub Transport and Edge Transport servers), and will stop new message submission if these resources run low. Existing messages in the queue will continue to be delivered, and when resource utilization returns to normal, message submission resumes. This feature is called back pressure.

 Solution: To remedy the issue, you will need to reconfigure the Transport Service by doing the following:

1-    Open the “EdgeTransport.exe.config” file, which is located under the C:\Program Files\Microsoft\Exchange Server\Bin directory.

2-    Disable resource monitoring or change the monitoring configuration:

Open the “EdgeTransport.exe.config” file with Notepad and change the resource values; or an easier option is to just disable the monitoring completely.

To change the resource values, the string should go from: add key=“EnableResourceMonitoring” value=”true” /
To add key=“EnableResourceMonitoring” value=”false” /

Once this is done, save the file and restart the Microsoft Exchange Transport Service.


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Abderrahim Ibnou El Kadi

Abderrahim Ibnou El Kadi

Abderrahim is affectionately known as Al because we mangle his real name. As our support lead, Al brings to his role more than 10 years of world-wide experience in the IT industry, having worked in Canada, the United States and Morocco (in 3 languages, no less). He is a natural fixer of things and will go above and beyond to solve a problem. His passion for astronomy explains his Zen-like calm and wise-beyond-his-years attitude.

Comments (5)

  • Richard Greenborough


    Ben, if you disable the resource monitoring in Exchange, it could lead to resource exhaustion (ie: out of disk space for instance).

    It’s better to look in the event viewer for the cause on the exchange server and then remedy it than disabling the resource monitoring.


  • Haukur Kristinsson


    (Y). Better to disable EnableResourceMonitoring and use monitoring tools like nagios to monitor your disks, before going into resource exhaustion 😉


  • yik


    i have the same problem, but i have lots of disk space and ram (1.4TB hdd and 8GB RAM)…..all external mail stuck on queue out of sudden and i have to restart the transport service to let the msg get thru…any idea?


  • Irfad Razick


    Thank you, this worked! I had only 1 GB left in the drive xD


  • Antony


    Thank you Mr. Abderrahim Ibnou El Kadi. Emails are coming in. Well done.


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