Download the installer for your operating system below.
macOS (.dmg) — the build is ad-hoc signed but not notarized (no paid Apple
account), so the first launch is blocked by Gatekeeper. After dragging Postmaster to
Applications, right-click the app → Open (then Open again), or run:
xattr -dr com.apple.quarantine /Applications/Postmaster.app
(Installing via Homebrew does this for you.)
Windows (.msi / -setup.exe) — unsigned, so SmartScreen shows "Windows protected
your PC" → click More info → Run anyway.
Linux — .AppImage (chmod +x then run) or .deb. No extra steps.
Once installed, Postmaster updates itself: it checks this releases page on launch
and installs newer signed builds in place, so you only do the manual install once.