Modernized hMailServer 6.0 - first regression-validated build.

Toolchain: VS2026 (v145), OpenSSL 4.0.1, Boost 1.91, PostgreSQL 18.3 libpq, .NET Framework 4.8.1. Database version 6001 (upgrade from 5.7 supported via DBUpdater).

New in 6.0: MTA-STS + DANE/DNSSEC outbound TLS policy, ARC sealing, TLS-RPT reporting, ACME (Let's Encrypt) with auto-apply, REST admin API, MTA-STS/autoconfig/autodiscover hosting, Prometheus metrics, JSON logging, PBKDF2 password hashing with transparent rehash, Ed25519 DKIM, DMARC, IMAP MOVE/ID/SPECIAL-USE, 8BITMIME, Administrator dashboard + TOTP 2FA, TLS 1.2/1.3 defaults.

Validation: full regression suite - 898 tests, 895 passed, 0 code failures. Validated with live SpamAssassin (JAM Windows build), ClamAV 1.5.2 and all optional features enabled. The 3 non-passing tests are environment-bound: 2 require an unfiltered DNS resolver for SURBL test queries, 1 requires the service-based SpamAssassin variant. Includes fix for a latent CStdStr::FormatV buffer-count bug that crashed the service.

Install: run the installer; internal database (SQL CE 4.0) or external MySQL/MSSQL/PostgreSQL. See IMPLEMENTATION-NOTES.md for the feature/INI reference.

License: AGPLv3. Based on hMailServer by Martin Knafve.