Event ID: 452 4.3.1 Insufficient System Resources Exchange- Solved

Written By Ashwani Tiwari
Anuraag Singh
Approved By Anuraag Singh
Published On July 21st, 2022
Reading Time 5 Minutes Reading

There is a very common error faced by the Microsoft Exchange Server administrators reporting insufficient system resources. Or sometimes, the same error is encountered in a different way also like Event ID 452 4.3.1 Insufficient System Resources Exchange. Moreover, whenever an IT user looks at the server, he or she is unable to identify the obvious root cause. Therefore, in order to know all about the about this error in Exchange and how it can be fixed, continue reading the blog.

Exchange Server Event ID 452 4.3.1 – User Scenarios:

“Last night, I was preparing a presentation on Exchange 2010 transport. At that point of time, when I was trying to telnet the SMTP port of Exchange 2010 Hub Transport Server, I received the error displayed below:

Event ID: 452 4.3.1, Insufficient system resources

452 4.3.1 error in exchange

I did not get what has exactly happened? where I am lacking behind? In order to understand the issue in a better way, I tried to send an email with the help of telnet from CMD. As I run the command mail on the server, it returned an error i.e., 452 4.3.1 insufficient system resources. Can anyone explain me what is exactly going on and how it can be fixed?”

Apart from this, there is another case:

“Recently, one of the Exchange administrators complained that he is facing difficulty in receiving emails in MS Exchange 2010. However, the protocol logs reported an error message “452 4.3.1 Insufficient system resources in Exchange”.

In addition to this, when its Application Event Log is checked to diagnose, it displays an Event ID 15006 from MSExchangeTransport:

Microsoft Exchange Transport is rejecting message submissions because the available disk space has dropped below the configured threshold.


exchange error

According to this event, it is clear that disk space of queued database logging and physical memory of load resources were under the pressure. This is the reason why mail submission was disabled because of the back pressure. Therefore, users want to know what action needs to be taken to get rid off this 452 4.3.1 insufficient system resources Exchange error.

Why Users Encounter Exchange Error 452 4.3.1?

If users are facing this issue, then there must be some or another valid reason behind it. However, all of them are mentioned below:

  • There is a shortage of free disk space on which Exchange Hub Transport is queued.
  • Back pressure can also be one of the reason as it keeps track of free disk space or when important resources are under the pressure.
  • When the volume on which Exchange is used has dropped down below or exceeds the already specified free disk space threshold.

If the specified threshold limit exceeds, then Exchange can:

  • In case of Medium Threshold (90%): It will stop getting emails over SMTP from external senders.
  • In case of High Threshold (99%): The mail flow is stopped completely to be processed.

exchange issues

What All are the Corrective Measures?

If a user is receiving this error then, it is suggested to check that the server has enough disk space or not. If yes, then the message is cleared automatically.

However, if the disk space is not full or not enough, then deleting emails from the disk will not going to help out. It is because whenever emails are removed from the inbox, the Exchange Server does not remove emails and free up space on the disk immediately.

Hence, in order to correct this issue, a user has to fix disk space issue by moving mailboxes, clearing logs from the disk, or deleting unused files from the drive.

Other manual tricks that an Exchange Administrator can use are:

  1. First of all, clean all trash from the disk
  2. Turn off Back Pressure monitoring manually (Can be used as a last option)
  3. Move all transport queues i.e., mail.que to some another disk that has more disk space available.
  4. Now, as discussed above, Back Pressure is one of the important reason behind this 452 4.3.1 insufficient system resources Exchange error. It is by default enabled, so before disabling, it is important to know about it.

What Exactly is Back Pressure in Exchange?

Back pressure is a feature of the Microsoft Exchange Transport service to monitor the system resource. It basically exists on the Mailbox servers and the Edge Transport servers. Its main and only motive is to detect and monitor the important system resources.

For example, hard drive space and memory are in pressure or not. If yes, take an action and prevent the server from being completely unavailable.

Level of Overused:

In addition to this, for each monitored resource, a level of pressure or resource utilization is specified. For example, if it is:

  • Low or Normal: The monitored resource is not overused yet.
  • Medium: The monitored resource is somewhat overused.
  • High: The monitored resource is under pressure and badly overused.

Action Undertaken by Back Pressure

If any of the resources are under pressure or overused, then there are some actions taken by the back pressure. Here, without distracting from the topic, we will talk about database used space only:

Database Used Space

  • Medium: Reject incoming message and message submission in the non-Exchange server is paused.
  • High: All medium level plus discard incoming messages from other Exchange Server. In addition, it avoids message submission from other mailboxes.

Lets Conclude

Back pressure might result in some serious problems in an Exchange Server. It can be because of interruptions in message delivery. Therefore, corrective actions need to be taken in such cases and avoid event id 452 4.3.1 insufficient system resources Exchange errors efficiently.


By Ashwani Tiwari

Being a Chief Technical Analyst, I am aware of the technicalities faced by the user while working with multiple technologies. So, through my blogs and articles, I love to help all the users who face various challenges while dealing with technology.