If you see this error in /webmail:
ERROR (2): Header may not contain more than a single header, new line detected. (/webmail/inc/inc.php:169)
edit /var/www/html/webmail/inc/inc.php, go to line 169. Change
Header("Expires: Wed, 11 Nov 1998 11:11:11 GMT\r\n".
"Cache-Control: no-cache\r\n".
"Cache-Control: must-revalidate");
to
Header("Expires: Wed, 11 Nov 1998 11:11:11 GMT");
Header("Cache-Control: no-cache");
Header("Cache-Control: must-revalidate");
Save, and exit.