autodiscover

Allows email server autodiscovery with Outlook and Thunderbird on non-Exchange servers.

If you host an email server, you want it to be compatible with all kinds of clients. You don't want your end user to enter manually the email configuration for their email address.

With Thunderbird and software using the same standards, you can just use the autoconfig file. Sadly, on Outlook, Apple Mail and Apple phones, it doesn't work the same.

Outlook uses an undocumented, proprietary protocol called Autodiscover, that is made to only work on Outlook Exchange servers. This software attempts to reimplement this protocol, so your free-software based mail server works out-of-the-box with Outlook clients.

Apple mobile phones uses the mobileconfig file which is documented but very messy and incompatible with other "usual" installation methods.

Supported clients

• Thunderbird
• Apple Mail (check out #7 to see how it works)
• Outlook clients (2003, 2007, 2010, 2013) – partially tested

Unsupported (yet)

• Outlook clients (2016, 2019, Office 365), using Autodiscover V2 protocol

Setup

The application

Docker

Download the docker image:

docker pull git.lacontrevoie.fr/lacontrevoie/autodiscover:latest

Copy config.toml in a dedicated folder and fill the values according to your email setup.

Basic docker compose file:

services:
  autodiscover:
    image: git.lacontrevoie.fr/lacontrevoie/autodiscover:latest
    volumes:
      - ./config.toml:/run_dir/config.toml:ro
    read_only: true
    security_opt:
        - no-new-privileges

This software does not need any write access. The Docker image also makes it run with an unprivileged user for hardened security.

Manual build

Git clone then build with Cargo, like a regular Rust application.

The server

Run the application on your server, then make it listen to those two virtual hosts:

• autodiscover.mydomain.com
• autoconfig.mydomain.com

The best way to do so is to use a reverse proxy, which can also handle HTTPS.

DNS records

You have to create a lot of DNS records to make autodiscovery work for all clients. Be sure to double check every entry.

• Replace mydomain.com with your own domain.
• Replace 1.2.3.4 with your server's IP address.

On the mail server's domain

All of those entries should be recorded on your main domain.

autoconfig          86400 IN CNAME  autodiscover.mydomain.com.
autodiscover        86400 IN CNAME  autodiscover.mydomain.com
_imap._tcp          86400 IN SRV    0 0 143 mail.mydomain.com.
_imaps._tcp         86400 IN SRV    0 0 993 mail.mydomain.com.
_pop3._tcp          86400 IN SRV    0 0 110 mail.mydomain.com.
_pop3s._tcp         86400 IN SRV    0 0 995 mail.mydomain.com.
_smtp._tcp          86400 IN SRV    0 0 25 mail.mydomain.com.
_smtps._tcp         86400 IN SRV    0 0 465 mail.mydomain.com.
_submission._tcp    86400 IN SRV    0 0 587 mail.mydomain.com.
_autodiscover._tcp  86400 IN SRV    5 0 443 autodiscover.mydomain.com

On a "customer" domain

Those entries should be added to any other domain using your mail server.

autoconfig          86400 IN CNAME 	autodiscover.mydomain.com
autodiscover        86400 IN CNAME 	autodiscover.mydomain.com
_autodiscover._tcp  86400 IN SRV 	5 0 443 autodiscover.mydomain.com

You also need to generate a TLS certificate for each customer domain (specifically, for autoconfig and autodiscover subdomains).

This project is fully and shamelessly inspired of the following projects:

• https://github.com/Earl0fPudding/outlook-autodiscover-nginx
• https://github.com/gronke/email-autodiscover
• https://github.com/Tiliq/autodiscover.xml

This software is a rewrite of those projects in Rust with the Actix framework, so no PHP interpreter or Javascript is needed.