Skip to content
  • Categories
  • Recent
  • Popular
  • Tags
  • Users
  • Groups
  • Documentation
  • Downloads
  • Report a bug
  • Commercial support
Skins
  • Light
  • Brite
  • Cerulean
  • Cosmo
  • Flatly
  • Journal
  • Litera
  • Lumen
  • Lux
  • Materia
  • Minty
  • Morph
  • Pulse
  • Sandstone
  • Simplex
  • Sketchy
  • Spacelab
  • United
  • Yeti
  • Zephyr
  • Dark
  • Cyborg
  • Darkly
  • Quartz
  • Slate
  • Solar
  • Superhero
  • Vapor

  • Default (No Skin)
  • No Skin
Collapse
hMailServer Community Forum
hMailServer 6.3.3 — signed 15 September 2026, Windows and Linux, database schema 6040, and a drop-in upgrade from any 5.x install.Download 6.3.3 Documentation
  1. Support and discussion for hMailServer
  2. Running hMailServer
  3. TLS, certificates & deliverability
  4. Let's Encrypt certificates are automatic: the built-in ACME v2 client

Let's Encrypt certificates are automatic: the built-in ACME v2 client

Scheduled Pinned Locked Moved TLS, certificates & deliverability
acmelets-encrypttlscertificates
1 Posts 1 Posters 4 Views 1 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • P
    P
    Progressiverobot
    hMailServer Team
    wrote last edited by
    #1

    hMailServer has an ACME v2 client built in (RFC 8555). It obtains a free certificate, installs it, assigns it to your TLS ports, renews it before expiry and reloads it. No restart, no scheduled task, no external client.

    Configure it under Settings → Security → Certificates (ACME), or in hMailServer.INI:

    AcmeEnabled=1
    [email protected]
    AcmeDomains=mail.yourcompany.com,mta-sts.yourcompany.com,autoconfig.yourcompany.com
    AcmeHttpPort=80
    AcmeReuseKey=1
    

    AcmeEnabled ships as 0. AcmeDirectoryUrl defaults to https://acme-v02.api.letsencrypt.org/directory.

    Two requirements. Port 80 must be reachable from the internet, because that is how the http-01 challenge proves you control the name. Every name in AcmeDomains must already resolve to this server before you switch it on. If you also host MTA-STS or client autoconfiguration, put mta-sts.<domain>, autoconfig.<domain> and autodiscover.<domain> in AcmeDomains so one certificate covers them.

    After issuance. The server creates or updates a certificate record named ACME (automatic) and assigns it to every TLS-enabled listener that has none of its own, logging each assignment. A listener the assignment could not be saved for is reported as a High 6100 rather than logged as a success, because a port left without a certificate accepts no TLS at all. That is the error to alert on.

    Renewal. The renewal window is two thirds of the certificate lifetime, plus ARI. That is why there is nothing left to schedule. Files live in Data\ACME on Windows and /var/lib/hmailserver/ACME/ on Linux: the account key, fullchain.pem and privkey.pem. Back that directory up with the rest of Data\. If a restore misses it the client re-issues, but the new key invalidates any TLSA records you have published.

    Leave AcmeReuseKey=1. Keeping the same private key across renewals is what keeps published TLSA records valid.

    Linux. Port 80 works without root. CAP_NET_BIND_SERVICE on the unit is what allows the bind. The default certificate directory is <DataFolder>/ACME, which is inside ReadWritePaths. Point AcmeCertificateDirectory elsewhere and you must add that path to ReadWritePaths with a drop-in, or issuance fails on a read-only filesystem.

    If it never worked for you. The built-in client had never once succeeded against real Let's Encrypt until 6.2.24 (#34). Boulder pretty-prints its JSON and the challenge locator searched for the compact spelling. 6.2.25 then fixed issuance and renewal ending the process (#93). If you gave up on this on an older build, it is worth another look.

    Another CA. Leave AcmeEnabled=0, add the PEM certificate and key under Settings → Security → SSL certificates, then assign it to ports under Settings → Network → TCP/IP ports. On Linux, an external client that replaces the PEM files in place needs POST /api/v1/server/reinitialize or a restart before the new files are served.

    Chapter 9, encryption and certificates: https://www.progressiverobot.com/hmailserver-documentation/#9-encryption-and-certificates
    Report problems: https://gitlab.com/Progressiverobot/hmailserver

    1 Reply Last reply
    0

    Hello! It looks like you're interested in this conversation, but you don't have an account yet.

    Getting fed up of having to scroll through the same posts each visit? When you register for an account, you'll always come back to exactly where you were before, and choose to be notified of new replies (either via email, or push notification). You'll also be able to save bookmarks and upvote posts to show your appreciation to other community members.

    With your input, this post could be even better 💗

    Register Login
    Reply
    • Reply as topic
    Log in to reply
    • Oldest to Newest
    • Newest to Oldest
    • Most Votes


    • Login

    • Don't have an account? Register

    • Login or register to search.

    hMailServer Community

    The community support forum for hMailServer — the free, open-source mail server for Windows and Linux — maintained by Progressive Robot Ltd. The software is AGPL-3.0 and stays that way; this is where it is discussed, debugged and documented.

    The software

    • Documentation
    • Downloads
    • hMailServer 6.3
    • Source on GitLab

    Getting help

    • Forum rules
    • About this forum
    • Support plans
    • Pay monthly support
    • Talk to Progressive Robot

    Legal

    • Privacy policy
    • Terms and conditions
    • Cookie policy

    Progressive Robot Ltd · 220 Chester Business Park, Heronsway, Chester, Cheshire CH4 9GB, United Kingdom · +44 (0)1244 911212 · [email protected] · VAT 506152326

    Powered by NodeBB

    • First post
      Last post
    0
    • Categories
    • Recent
    • Popular
    • Tags
    • Users
    • Groups
    • Documentation
    • Downloads
    • Report a bug
    • Commercial support