mxlookup Plugin for Roundcube

The mxlookup plugin for Roundcube performs a lookup of the login user's MX records and dynamically chooses the imap_host based on the retrieved MX records. This allows for flexible configuration of the IMAP host based on the user's domain.

Features

• Retrieves the MX records for the user's domain
• Filters out MX records containing the word "relay"
• Selects the lowest priority MX record as the imap_host value
• Validates the imap_host IP address against a whitelist
• If the user's MX records don't point directly to MXroute, they can create a TXT record named "mxwebmail" with the contents being the hostname for one of our servers (example: "arrow.mxrouting.net"). The plugin will pick up that TXT record if it fails on the MX checks.

Requirements

• Tested on Roundcube version 1.6.7

Installation

1. Clone the mxlookup plugin repository into your Roundcube plugins directory:

   git clone https://github.com/mxroute/mxlookup

2. Add "mxlookup" to the plugins array in your Roundcube config/config.inc.php file:

   $config['plugins'] = array('mxlookup');

3. In the same config/config.inc.php file, set the imap_host configuration option to a default value. For example:

   $config['imap_host'] = 'default';

This ensures that the user does not see a "server" box on the login form.

4. Create a whitelist.txt file in the plugins/mxlookup directory. This file should contain a list of approved IP addresses (one per line) that are allowed to be used as imap_host values. This whitelist prevents the plugin from being utilized by users on unauthorized servers.

Customization

• Filtering MX Records

The original mxlookup plugin was developed for MXroute. If you need to modify the filtering of MX records, you can adjust the following code snippet in plugins/mxlookup/mxlookup.php:

`// Filter out any MX records containing the word "relay"
$mx_records = array_filter($mx_records, function ($record) {
    return strpos($record['target'], 'relay') === false;
});`

You can modify or remove this code snippet based on your specific requirements.