Exchange 2019 not sending or receiving emails after CU 15 installation

Hi @DANIEL DIGREGORIO ,

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

Here are some suggestions for you for on-prem Exchange mail flow issues:

1. Do your users only have send/receive issues with Outlook client side? Do you try to send and receive from OWA with Microsoft Edge browser? What about internal emails that send between on-prem Exchange sender and recipient?
2. Starting with Exchange 2019 CU14, Windows Extended Protection (EP) feature on the Exchange server will be enabled by default. There are some prerequisites and unsupported scenario for EP, and Outlook connection could be affected. We could disable EP manually after upgrading to Exchange 2019 CU15. .\ExchangeExtendedProtectionManagement.ps1 -DisableExtendedProtection Then try to reset IIS on all your Exchange servers. iisreset For more information about Extended protection and the script to disable EP, please check: Exchange Server support for Windows Extended Protection | Microsoft Learn ExchangeExtendedProtectionManagement - Microsoft - CSS-Exchange
3. You can use the following command to check on-prem message tracking log for email deliver process. Then check if these emails are stuck on Exchange server, or just cannot be updated to Outlook client side. Get-transportservice| Get-MessageTrackingLog -MessageSubject “email_subject” |sort-object timestamp When there is one log entry that eventid shows DELIVER, it means email is delivered to a local on-prem mailbox successfully.

For more information about message tracking log, please check:

Message tracking | Microsoft Learn

Search message tracking logs | Microsoft Learn

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