---
title: "hMailServer 6.2.1: PIPELINING, SMTPUTF8, DSN and SRS"
url: https://www.hmailserver.co.uk/topic/28214/hmailserver-6.2.1-pipelining-smtputf8-dsn-and-srs
author: "Progressiverobot"
published: 2026-06-14T09:15:18.000Z
updated: 2026-06-14T09:15:18.000Z
category: "Announcements & releases"
tags: ["release","smtp","bugfix"]
site: hMailServer Community Forum
---

# hMailServer 6.2.1: PIPELINING, SMTPUTF8, DSN and SRS

6.2.1 completed Track B4, the deliverability and modern SMTP standards work. It added four ESMTP extensions, SRS for forwarded mail and SMTP rate shaping.

- **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.

[Full release notes, checksums and signatures](https://www.progressiverobot.com/hmailserver-downloads/)