How to fix Exchange 452 4.3.1 Insufficient system resources

The first symptom : no incoming mails in your Exchange Organisation.
The first test to make : try to test your incoming SMTP service using telnet.
If you have the following result, you're reading the right post !

452 4.3.1 Insufficient system resources

If you have a quick look in your event log, you will find a 15002 event message, explaining you that your disk space is low. Here we are.
Different security levels are set in exchange, chained to different reactions : http://technet.microsoft.com/en-us/library/bb397220(EXCHG.80).aspx

Two ways to get out of this issue :

1. increase disk space
2. disable the Back Pressure Feature

For the first point, no lesson, just act as you are used to.
For the second point : Back Pressure Feature.
Differents triggers :

• Disk space, memory, ...

Three levels :

• Normal Action: The Exchange Server 2007 Server accepts new connections and messages.
• Medium Action: The resources sre starting to be overused. Back pressure is applied to the server in a limited manner. Messages from senders in the authoritative domain can flow, but the server will reject new connections and messages from other sources.
• High Action: A resource is being overused. All message flow will stop and the server will reject all new connections and messages.

To disable the Back Pressure Feature, you have to edit the file located in the bin folder of your exchange server : EdgeTransport.exe.config
Locate the EnableResourceMonitoring param and put the value to "false".
Restart the Exchange Transport Service using the exchange shell :

Restart-Service msExchangeTransport

Sources :

• http://www.msexchange.org/articles_tutorials/exchange-server-2007/management-administration/understanding-back-pressure-feature-exchange-server-2007.html
• http://www.hyperv.fr/2010/10/04/exchange-hub-transport-452-431-insufficient-system-resources-12961.html