Use PostgreSQL to set the identity for new users in RoundCube.

new_user_identity_pgsql.php

<?php
/**
 * New user identity
 *
 * Populates a new user's default identity from LDAP on their first visit.
 *
 * This plugin requires that a working public_ldap directory be configured.
 *
 * @version @package_version@
 * @author Kris Steinhoff
 * @license GNU GPLv3+
 *
 * Example configuration:
 *
 *  // The id of the address book to use to automatically set a new
 *  // user's full name in their new identity. (This should be an
 *  // string, which refers to the $config['ldap_public'] array.)
 *  $config['new_user_identity_addressbook'] = 'People';
 *
 *  // When automatically setting a new users's full name in their
 *  // new identity, match the user's login name against this field.
 *  $config['new_user_identity_match'] = 'uid';
 */
class new_user_identity_pgsql extends rcube_plugin
{
    public $task = 'login';

    private $db;

    function init()
    {
        $this->add_hook('user_create', array($this, 'lookup_user_name'));
    }

    function lookup_user_name($args)
    {
        $rcmail = rcmail::get_instance();

        $db_host = $rcmail->config->get('new_user_identity_pgsql_host');
        $db_user = $rcmail->config->get('new_user_identity_pgsql_user');
        $db_pass = $rcmail->config->get('new_user_identity_pgsql_pass');
        $db_name = $rcmail->config->get('new_user_identity_pgsql_database');
        $db_query = str_replace ( '%u', $args['user'], $rcmail->config->get('new_user_identity_pgsql_query') );
            
        if ( $dbconn = pg_connect("host=$db_host user=$db_user password=$db_pass dbname=$db_name") ) {
            $result = pg_query ( $db_query );
            if ( $result ) {
                if ( pg_num_rows ( $result ) == 1 ) {
                    $user_email = pg_fetch_result ( $result, 0, 0 );
                    
                    if (!$args['user_email'] && strpos($user_email, '@')) {
                        $args['user_email'] = rcube_utils::idn_to_ascii($user_email);
                    }

                    $args['user_name'] = pg_fetch_result ( $result, 0, 1 );
                }

                pg_free_result ( $result );
            }

            pg_close ( $dbconn );

            return $args;
        }
    }
}

class new_user_identity_pgsql_backend
{
    function __construct($p, $debug, $mail_domain, $search)
    {
        parent::__construct($p, $debug, $mail_domain);
        $this->prop['search_fields'] = (array)$search;
    }
}