Exchange Server 2019 – How to Improve Mail Flow Stability Under Heavy Load?

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Exchange Server 2019 – How to Improve Mail Flow Stability Under Heavy Load?

Montez Martha 40

I’m looking for guidance on optimizing mail flow performance in Exchange Server 2019 after noticing intermittent delays when the server is under moderate or heavy load. Message Tracking shows that emails occasionally sit in the Submission or Categorizer stage longer than expected, even though CPU, RAM, and disk usage look normal.

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Answer 1

Hi @Montez Martha

Thank you for posting your question in Microsoft Q&A.

Could you check the current transport rule configuration on your server?

I found a relevant article from Q&A AI answer suggesting that this issue might be caused by rules using the “Matches Patterns” condition. This condition involves a complex and resource-intensive process.

To reduce latency, consider simplifying these rules by replacing “Matches Patterns” with “Contains Words” conditions. You could follow these steps:

Review existing transport rules and identify those using “Matches Patterns.”

Avoid regex-heavy conditions like "AnyOfRecipientAddressMatchesPatterns" or "FromAddressMatchesPatterns", as they require intensive processing and can delay messages even for small recipient lists.

Replace with simpler "Contains Word" conditions to reduce latency.

To review rules, run:

Get-TransportRule | Format-List Name, Conditions

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You can refer via: Slow mail delivery in Exchange that has transport rules configured - Exchange | Microsoft Learn

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Answer 2

To improve mail flow stability in Exchange Server 2019 under heavy load, consider the following optimizations:

Optimize Transport Rules: If you have transport rules configured, avoid using conditions that involve "Matches Patterns" as they can cause significant delays in message processing. Instead, use "Contains Word" which is less resource-intensive and can improve performance.
Adjust SMTP Connector Settings: If your server primarily sends to Exchange Online, you can modify the following settings to enhance performance:
- SmtpConnectorQueueMessageCountThresholdForConcurrentConnections: Lowering this threshold (default is 20) can help create new connections sooner. Setting it to 2 can significantly reduce queue sizes.
- MaxPerDomainOutboundConnections: Increase the maximum number of concurrent connections to a single domain from the default of 20 to a higher value, such as 40, to improve throughput.
- MessageRetryInterval: Reducing the retry interval for messages after connection failures can help in faster recovery from issues.
Monitor Submission Queue: Keep an eye on the Submission queue length. A large number of messages in this queue may indicate that the categorizer is struggling to process messages, leading to delays. Adjusting the settings mentioned above can help alleviate this pressure.
Back Pressure Management: Understand how Exchange manages back pressure. If memory utilization is high, Exchange may throttle incoming connections, which can lead to delays. Ensure that your server's resources are adequately monitored and managed to prevent back pressure situations.

Implementing these strategies can help mitigate delays and improve the overall mail flow performance in your Exchange Server environment under load.

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Exchange Server 2019 – How to Improve Mail Flow Stability Under Heavy Load?

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