wan24-AutoDiscover

This is a micro-webservice which supports a small part of the Microsoft Exchange POX autodiscover standard, which allows email clients to receive automatic configuration information for an email account.

It was created using .NET 8 and ASP.NET. You find a published release build for each published release on GitHub as ZIP file download for self-hosting.

The webservice is designed for working with dynamic MTA configurations and tries to concentrate on the basics for fast request handling and response. All required informations will be held in memory, so no database or filesystem access is required for request handling.

Usage

Pre-requirements

This app is a .NET 8 app and needs the ASP.NET runtime environment.

How to get it

For example on a Debian Linux server:

mkdir /home/autodiscover
cd /home/autodiscover
wget https://github.com/nd1012/wan24-AutoDiscover/releases/download/v1.2.0/wan24-AutoDiscover.v1.2.0.zip
unzip wan24-AutoDiscover.v1.2.0.zip
rm wan24-AutoDiscover.v1.2.0.zip

appsettings.json

The appsettings.json file contains the webservice configuration. The DiscoveryConfig is a wan24.AutoDiscovery.Models.DiscoveryConfig object. An example:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "Kestrel": {
    "Endpoints": {
      "AutoDiscover": {
        "Url": "http://127.0.0.1:5000"
      }
    }
  },
  "AllowedHosts": "*",
  "DiscoveryConfig": {
    "PreForkResponses": 10,
    "KnownProxies": [
      "127.0.0.1"
    ],
    "Discovery": {
      "localhost": {
        "AcceptedDomains": [
          "wan24.de",
          "wan-solutions.de"
        ],
        "Protocols": [
          {
            "Type": "IMAP",
            "Server": "imap.wan24.de",
            "Port": 993
          },
          {
            "Type": "SMTP",
            "Server": "smtp.wan24.de",
            "Port": 587
          }
        ]
      }
    }
  }
}

Since the webservice should only listen local and be proxied by a real webserver (like Apache2), there is a wan24.AutoDiscover.Models.DomainConfig for localhost, which produces POX response for the allowed domains wan24.de and wan-solutions.de in this example (you should use your own domain names instead).

The email client configuration will get an IMAP and a SMTP server pre- configuration, which contains the alias of the requested email address as login name and has all the other defaults from a wan24.AutoDiscover.Models.Protocol instance.

With the PreForkResponses value you can define a number of pre-forked POX response XML documents to serve faster responses.

Any change to this file will cause an automatic reload of the DomainConfig section.

For serving a request, the DomainConfig will be looked up

1. by the email address domain part
2. by the served request hostname
3. by any DomainConfig which has the email address domain part in the AcceptedDomains property, which contains a list of accepted domain names
4. by the DomainConfig with an empty domain name as key

Any unmatched DomainConfig will cause a Bad request http response.

Find the online documentation of the used types here:

• DiscoveryConfig
• DomainConfig
• Protocol

Run as systemd service

On a Debian Linux host you can run the wan24-AutoDiscover microservice using systemd:

dotnet wan24AutoDiscover.dll autodiscover systemd > /etc/systemd/system/autodiscover.service
systemctl enable autodiscover
systemctl start autodiscover
systemctl status autodiscover

Apache2 proxy setup

Create the file /etc/apache2/sites-available/autodiscover.conf:

<VirtualHost [IP]:443>
        ServerName [DOMAIN]
        SSLEngine on
        SSLCertificateFile /path/to/fullchain.pem
        SSLCertificateKeyFile /path/to/privkey.pem
        ProxyPreserveHost On
        ProxyPass / http://127.0.0.1:5000/
        ProxyPassReverse / http://127.0.0.1:5000/
</VirtualHost>

Replace [IP] with your servers public IP address and [DOMAIN] with your domain name which you'd like to use for serving autodiscover.

Then activate the proxy:

a2enmod proxy
a2ensite autodiscover
systemctl restart apache2

POX request and response

This is an example POX request to /autodiscover/autodiscover.xml:

<Autodiscover xmlns="https://schemas.microsoft.com/exchange/autodiscover/outlook/requestschema/2006">
   <Request>
     <EMailAddress>alias@wan24.de</EMailAddress>
     <AcceptableResponseSchema>https://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a</AcceptableResponseSchema>
   </Request>
 </Autodiscover>

The response with the demo appsettings.json:

<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
    <Response xmlns="https://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a">
        <Account>
            <AccountType>email</AccountType>
            <Action>settings</Action>
            <Protocol>
                <Type>IMAP</Type>
                <Server>imap.wan24.de</Server>
                <Port>993</Port>
                <LoginName>alias</LoginName>
                <SPA>off</SPA>
                <SSL>on</SSL>
                <AuthRequired>on</AuthRequired>
            </Protocol>
            <Protocol>
                <Type>SMTP</Type>
                <Server>smtp.wan24.de</Server>
                <Port>587</Port>
                <LoginName>alias</LoginName>
                <SPA>off</SPA>
                <SSL>on</SSL>
                <AuthRequired>on</AuthRequired>
            </Protocol>
        </Account>
    </Response>
</Autodiscover>

Required DNS configuration

In order to make autodiscover working in an email client, you'll need to create a SRV record for your email domain - example:

_autodiscover._tcp      1D IN SRV 0 0 443 [MTA-DOMAIN].

The domain wan24.de uses this record, for example:

_autodiscover._tcp      1D IN SRV 0 0 443 mail.wan24.de.

CLI API

The wan24-AutoDiscover has a small built in CLI API, which can do some things for you:

Create a systemd service file

dotnet wan24AutoDiscover.dll autodiscover systemd > /etc/systemd/system/autodiscover.service

Parse a Postfix virtual configuration file

dotnet wan24AutoDiscover.dll autodiscover postfix < /etc/postfix/virtual > /home/autodiscover/postfix.json

Display version number

dotnet wan24AutoDiscover.dll autodiscover version

Upgrade online

Check for an available newer version only:

dotnet wan24AutoDiscover.dll autodiscover upgrade -checkOnly

NOTE: The command will exit with code #2, if an update is available online.

Upgrade with user interaction:

dotnet wan24AutoDiscover.dll autodiscover upgrade

Upgrade without user interaction:

dotnet wan24AutoDiscover.dll autodiscover upgrade -noUserInteraction

Display detailed CLI API usage instructions

dotnet wan24AutoDiscover.dll help -details

Login name mapping

If the login name isn't the email address or the alias of the given email address, you can create a login name mapping per domain and/or protocol, by defining a mapping from the email address or alias to the login name. During lookup the protocol mapping and then the domain mapping will be used by trying the email address and then the alias as key.

Automatic email address to login user mapping with Postfix

If your Postfix virtual email mappings are stored in a hash text file, you can create an email mapping from is using

dotnet wan24AutoDiscover.dll autodiscover postfix < /etc/postfix/virtual > /home/autodiscover/postfix.json

Then you can add the postix.json to your appsettings.json:

{
	...
  "DiscoveryConfig": {
	...
	"EmailMappings": "/home/autodiscover/postfix.json",
	...
  }
}

The configuration will be reloaded, if the postfix.json file changed, so be sure to re-create the postfix.json file as soon as the virtual file was changed. If you don't want that, set WatchEmailMappings to false.

Additionally watched files

You can set a list of additionally watched file paths to WatchFiles in your appsettings.json file. When any file was changed, the configuration will be reloaded.

Pre-reload command execution

To execute a command before reloading a changed configration, set the PreReloadCommand value in your appsettings.json like this:

{
	...
  "DiscoveryConfig": {
	...
	"PreReloadCommand": ["/command/to/execute", "argument1", "argument2", ...],
	...
  }
}

Automatic online upgrades

You can upgrade wan24-AutoDiscover online and automatic. For this some steps are recommended:

1. Create sheduled task for auto-upgrade (daily, for example)
2. Stop the service before installing the newer version
3. Start the service after installing the newer version

The sheduled auto-upgrade task should execute this command on a Debian Linux server, for example:

dotnet /home/autodiscover/wan24AutoDiscover.dll autodiscover upgrade -noUserInteraction --preCommand systemctl stop autodiscover --postCommand systemctl start autodiscover

If the upgrade download failed, nothing will happen - the upgrade won't be installed only and being re-tried at the next sheduled auto-upgrade time.

If the upgrade installation failed, the post-upgrade command won't be executed, and the autodiscover service won't run. This'll give you the chance to investigate the broken upgrade and optional restore the running version manually.

CAUTION: The auto-upgrade is being performed using the GitHub repository. There are no security checks at present - so if the repository was hacked, you could end up with upgrading to a compromised software which could harm your system!

The upgrade setup should be done in less than a second, if everything was fine.

Manual upgrade

1. Download the latest release ZIP file from GitHub
2. Extract the ZIP file to a temporary folder
3. Stop the autodiscover service, if running
4. Create a backup of your current installation
5. Copy all extracted files/folders excluding appsettings.json to your installation folder
6. Remove files/folders that are no longer required and perform additional upgrade steps, which are required for the new release (see upgrade instructions)
7. Start the autodiscover service
8. Delete the previously created backup and the temporary folder

These steps are being executed during an automatic upgrade like described above also.