Mail queue delivery delay

Hi,

I have an on-premises **Exchange Server 2019 CU15** with minimal email traffic. Recently, I've noticed that emails are arriving late.

I developed a **PowerShell script with ChatGPT** using `Get-MessageTrackingLog` to inform me by email when there are internal delays — specifically, the time from when the email arrives on the Exchange server (**event ID: Receive**) to when it is delivered to the user's mailbox (**event ID: Deliver**).

I’ve experienced delays ranging from **5 minutes to 60 minutes**.

The server also has **ESET Mail Security 12 for Exchange** installed. At first, I suspected ESET might be causing the delay, but after further testing, I believe the issue lies elsewhere.

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### Here is what I have already tried:

- Updated from **CU14 to CU15**
- **Uninstalled ESET** completely
- Added a new **vDisk** and created a new **mail database**, then moved all mailboxes
- **Reset performance counters**
- Checked event logs — they look **clean**

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Any feedback is highly appreciated!