I enable the system error reporting of Roundcube webmail config(main.inc.php) to show.
Here is the line:
// system error reporting: 1 = log; 2 = report (not implemented yet), 4 = show, 8 = trace
$rcmail_config['debug_level'] = 4;
Then I test by sending emails (with large font) coming from yahoo going to iredmail, I open roundcube webmail.
Here is the log error:
Warning: include(DOMDocument.php) [function.include]: failed to open stream: No such file or directory in /var/www/roundcubemail-0.3.1/program/include/iniset.php on line 99
Warning: include() [function.include]: Failed opening 'DOMDocument.php' for inclusion (include_path='/var/www/roundcubemail/:/var/www/roundcubemail/program:/var/www/roundcubemail/program/lib:/var/www/roundcubemail/program/include:.:/usr/share/pear:/usr/share/php') in /var/www/roundcubemail-0.3.1/program/include/iniset.php on line 99
Fatal error: Class 'DOMDocument' not found in /var/www/roundcubemail-0.3.1/program/lib/washtml.php on line 247