• PIPELINING (RFC 2920) advertised in EHLO.
• SMTPUTF8 / EAI (RFC 6531/6532): internationalised addresses accepted and relayed.
• ENHANCEDSTATUSCODES (RFC 2034): x.y.z codes on ESMTP replies.
• DSN (RFC 3461/3464): RET, ENVID, NOTIFY and ORCPT accepted. Per-recipient NOTIFY is honoured, and NOTIFY=NEVER suppresses failure DSNs.
• SRS (Sender Rewriting Scheme): HMAC-signed, reversible envelope rewrite on forwarding, for SPF alignment. Bounces are decoded back to the original sender. Opt-in via [Settings] SRSEnabled and SRSSecret.
• SMTP rate shaping, per-IP and per-destination, via [Settings] MaxSubmissionsPerIPPerMinute and MaxOutboundPerDestinationPerMinute. Both default to off.

One fix: Unicode::WideToMultiByte returned a trailing NUL that could corrupt DPAPI-protected stored secrets. The result is now trimmed to the exact byte length.

Everything new here defaults to off and is back-compatible, so the release changed nothing about an existing configuration until a setting was turned on. The build was clean, 0 warnings and 0 errors, with the SMTP regression suite and the in-server self-tests green.

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