Security update for Microsoft Exchange Server 2019 (KB5063222)

Hi @mara2021

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

Based on my research, the new Security update for Microsoft Exchange Server 2019 (KB5063222) will addresses multiple vulnerabilities including tampering, spoofing and information disclosure. It also resolves several issues, such as:

• eDiscovery export failures 
• Application pool hangs after MSIPC is enabled 
• Incorrect ACE modification via public folder managemen 

You can refer via:  

Description of the security update for Microsoft Exchange Server 2019: August 12, 2025 (KB5063222) - Microsoft Support 

For synchronization with Exchange Online on their iOS and Android mobile devices with on-premises user. I have not found any reports explicitly tie KB5063222 to mobile sync issues yet. 

However, I found an article mentioning that mobile devices could not connect to Exchange Online due to the following reason: 

• The device can't connect to the Internet service provider (ISP) or to the Internet. 
• The device isn't set up correctly. 
• The Exchange Online mailbox server that supports the connection isn't available because of maintenance or an outage issue. 

References: Mobile device can't connect via ActiveSync - Exchange | Microsoft Learn 

If you plan to deploy KB5063222 soon, I recommend testing it in a non-production environment first. Additionally, monitor mobile sync logs after the update to catch any potential issues that may arise. 

If you have any additional concern, feel free to comment below. I be more than happy to assist.

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