Upgrading your organization from current versions to Exchange Server SE

Srinivas1730 

1. Yes you can keep using WS2019; there is nothing specific to Exchange that replies on WS 2025 functionality (which makes sense at this point, because the OS is not widely available). There might be things in the future, but not aware of anything like this being planned as of now. Note, though that using a newer OS (such as WS2022 or WS2025) will give you longer support lifetime for the server OS that Exchange is running on, because Exchange does not support in-place upgrades of Windows OS between major versions once Exchange is installed.

2. Software Assurance (SA) is typically a part of the VL (Volume License) agreement. Please reach out to MSFT licensing / sales to get the most cost effective way of getting what you need. A few things that can help: Microsoft Volume Licensing - Microsoft Software Assurance and Frequently Asked Questions for Software Assurance. | Microsoft Learn

3. As we have mentioned - Exchange SE is going to be available through the volume licensing site which is where you'd be getting both the product keys and bits for things like CU updates. Without a subscription option (either VL or Microsoft 365) - you would not have access to updates and even if your server was already activated, you'd be technically out of licensing compliance.