Exchange Server 2016 CU23 Build Number Mapping (from Microsoft Learn)
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Target: autodiscover.almayadeen.net
Observed Build: 15.1.2507.59 (X-OWA-Version header)

Official Microsoft Build Numbers for CU23:
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15.1.2507.6   - CU23 RTM (Apr 20, 2022)
15.1.2507.9   - May22SU
15.1.2507.12  - Aug22SU
15.1.2507.13  - Oct22SU
15.1.2507.16  - Nov22SU
15.1.2507.17  - Jan23SU
15.1.2507.21  - Feb23SU
15.1.2507.23  - Mar23SU
15.1.2507.27  - Jun23SU
15.1.2507.31  - Aug23SU
15.1.2507.32  - Aug23SUv2
15.1.2507.34  - Oct23SU
15.1.2507.35  - Nov23SU
15.1.2507.37  - Mar24SU
15.1.2507.39  - Apr24HU
15.1.2507.43  - Nov24SU
15.1.2507.44  - Nov24SUv2
15.1.2507.55  - Apr25HU
15.1.2507.57  - May25HU
15.1.2507.58  - Aug25SU
15.1.2507.59  - Sep25HU  ← TARGET IS HERE (Sep 8, 2025)
15.1.2507.61  - Oct25SU  ← MISSING (CVE-2025-59249, CVE-2025-53782, CVE-2025-59248)
15.1.2507.63  - Dec25SU  ← MISSING (CVE-2025-64666, CVE-2025-64667)
15.1.2507.66  - Feb26SU  ← MISSING (CVE-2026-21527) — LATEST

Target is 3 security updates behind.
Last patched: September 8, 2025 (173 days ago as of Feb 28, 2026)

Source: https://learn.microsoft.com/en-us/exchange/new-features/build-numbers-and-release-dates