If you are getting following error while sending emails from squirrelmail.
Error: Message not sent. Server replied: Connection timed out 110 Can’t open SMTP stream.
Solution : If above case if you are having shell access then login to your server with root user, then edit
config file and do the changes as given below.
$useSendmail = false;
$useSendmail = true;
restart cpanel and exim service.