We should use hostname instead of localhost as IMAP host - makes box identity look good

config.inc.php

@@ -39,7 +39,7 @@ $config['log_driver'] = 'syslog';
 // For example %n = mail.domain.tld, %t = domain.tld
 // WARNING: After hostname change update of mail_host column in users table is
 //          required to match old user data records with the new host.
-$config['default_host'] = 'localhost';
+$config['default_host'] = trim(`hostname`);
 
 // provide an URL where a user can get support for this Roundcube installation
 // PLEASE DO NOT LINK TO THE ROUNDCUBE.NET WEBSITE HERE!