---
title: "hMailServer 6.0.0-B4: fixes the startup crash from the bundled VC++ runtime"
url: https://www.hmailserver.co.uk/topic/28212/hmailserver-6.0.0-b4-fixes-the-startup-crash-from-the-bundled-vc-runtime
author: "Progressiverobot"
published: 2026-06-12T20:44:23.000Z
updated: 2026-06-12T20:44:23.000Z
category: "Pre-release builds"
tags: ["prerelease","bugfix","windows","installer"]
site: hMailServer Community Forum
---

# hMailServer 6.0.0-B4: fixes the startup crash from the bundled VC++ runtime

This was a beta build of the 6.0 line. 6.0.0 was the production release. Nothing here should be installed today.

Build 3 shipped VC++ runtime DLLs that did not match the toolset the binaries were built with, and the service crashed at startup on fresh installs. This build corrects the installer payload.

The detail: hMailServer.exe is built with v145 (14.51), but build 3 bundled VS2019-era (14.25) VC++ runtime DLLs app-local in `Bin\`. Those app-local copies were loaded instead of the system runtimes, and the service died at startup with 0xC0000005 in `msvcp140!mtx_do_lock`, reached via boost regex and `std::mutex`. Fresh installs were the ones affected.

Changes in this build:

- The installer now ships Microsoft.VC145.CRT (14.51.36231), matching the build toolset. The stale Microsoft.VC142.CRT payload has been removed.
- The bundled 2015-era UCRT has been removed. It has been in-box since Server 2016 and Windows 10.
- `build/run-tests.ps1`: fixed a stdout/stderr pipe deadlock in the test runner.

The full regression gate ran against MariaDB on the MYSQL backend: 898 of 898 passed.

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