We recently got an email from the IT administrator of one of our customers that began with: "We are having an issue with external email! I have been sending test messages from an external account and they are not arriving, I have had no external email since7:31 pm Sunday. Nothing has been changed in our environment. Can you see anything from your side?" This email kicked off a series of troubleshooting steps on our end that ended up being caused by an issue I've been seeing for many years now, the mysterious Insufficient System Resources log message. This post will explain what that is and how to fix it.
Insufficient System Resources and Microsoft Exchange
To the best of my knowledge, the Insufficient System Resources message has these characteristics:
It primarily appears in Microsoft Exchange Server 2007, 2010, and 2013 environments
When that messages appears, Microsoft Exchange stops accepting inbound email
It can be very hard to troubleshoot
Technically, the '452 4.3.1 Insufficient system resources' message is caused by low memory or low free disk space. In my experience however, it's always been due to insufficient free disk space. The quickest way to get an Exchange server back on its feet is to free up disk space on the drive that stores the Exchange mailbox database. Depending on the version of Microsoft Exchange running, you'll need anywhere from 500MB to 4GB of free space. Further reading: Back Pressure and Exchange Server Transport error 452 4.3.1 Insufficient system resources
Hidden costs of Microsoft Exchange
The administration costs of running an on-premise Exchange server(s) are costly. Bewildering messages like Insufficient system resources is a prime example. It's no surprise then, that droves of customers have been migrating their Exchange environments to the cloud via Microsoft 365 (formerly Office 365). This trend has been going on for over ten years. One might assume there aren't many companies running Exchange anymore. In our experience at Paubox however, we've seen that many organizations still running Microsoft Exchange. Even in 2020, Microsoft Exchange remains a critical component of infrastructure within U.S. healthcare. Further reading: HIPAA Compliant Email: The Definitive Guide