Email not working with sendmail

I am trying to send email using sendmail.
Below is my email.php config file.

$config['protocol'] = 'sendmail';
$config['mailpath'] = '/usr/sbin/sendmail';
$config['charset'] = 'iso-8859-1';
$config['wordwrap'] = TRUE;


The email->print_debugger() gives

Exit status code: 64
Unable to open a socket to Sendmail. Please check settings.
Unable to send email using PHP Sendmail. Your server might not be configured to send mail using this method.

But sendmail works in CLI

Am I missing something?

Thanks in advance