452 4.3.1 Insufficient System Resources

Users mailboxes hosted on my Exchange 2016 started facing issues in receiving the email, and the sender were receiving an NDR with the following error:

I checked all of my Exchange Servers queue size C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue\mail.que is around 10GB on all of them.

Generally, it is referring to Back Pressure; in short, Back pressure is a system resource monitoring feature of the Microsoft Exchange Transport service that exists on Mailbox servers and Edge Transport servers.

Back Pressure monitors mainly the following criteria’s in Microsoft Exchange:

• DatabaseUsedSpace[%ExchangeInstallPath%TransportRoles\data\Queue]: Hard drive utilization for the drive that holds the message queue database
• PrivateBytes: The memory that’s used by the EdgeTransport.exe process.
• QueueLength[SubmissionQueue]: The number of messages in the Submission queue.
• SystemMemory: The memory that’s used by all other processes.
• UsedDiskSpace[%ExchangeInstallPath%TransportRoles\data\Queue]: Hard drive utilization for the drive that holds the message queue database transaction logs.
• UsedDiskSpace[%ExchangeInstallPath%TransportRoles\data]: Hard drive utilization for the drive that’s used for content conversion.
• UsedVersionBuckets [%ExchangeInstallPath%TransportRoles\data\Queue\mail.que]: The number of uncommitted message queue database transactions that exist in memory.

More details regarding Back Pressure is available on the below link:

https://docs.microsoft.com/en-us/Exchange/mail-flow/back-pressure?redirectedfrom=MSDN&view=exchserver-2019

Solution:

Run the following commands on your Exchange Server:

[PS] C:\Windows\system32>Get-TransportServer “servername” | fl

Make sure that “PipelineTracingEnabled = False”

If not then disable it by running the following command:

Set-TransportService Mailbox01 -PipelineTracingEnabled $false

Then Run,

[PS] C:\Windows\system32>Get-TransportConfig

Make sure that MaxDumpsterSizePerDatabase = 18 MB (18,874,368 bytes)

It should always be in MBs only.

Then check Queue:

[PS] C:\Windows\system32>Get-Queue

MessageCount = 0

Then stop Microsoft Exchange Transport Service:

Move “mail.que” to another location or Delete it.

Then Start the transport service again and check the mail flow.

For clearing Exchange Server logs, refer the below link:

https://ammar.cloud/clear-out-logs-for-exchange-2013-2016-2019/