Exchange 4.3.1 Insufficient System Resources Error

Problem:  Delivery to clients Exchange Mail server results in a defer message..

 dsn=4.3.1, status=deferred (host 1.2.3.4[client public mailserver ip] said: 452 4.3.1 Insufficient system resources (in reply to MAIL FROM command))

Analysis: Most common reason for this error is Back Pressure feature in Exchange Transport Service


Solution: You can reconfigure the Transport service by modifying the "EdgeTransport.exe.config" file which is located in ProgramFiles/Microsoft Exchange Bin folder.

Open Config file with notepad and change resource values or even easier to disable all together.

Example: add key="EnableResourceMonitoring" value="true" /

Change to: add key="EnableResourceMonitoring" value="false" /

Once complete, save the file and restart the Microsoft Exchange Transport service.

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