By default, our script sends e-mails using PHP's mail() function: http://www.php.net/manual/en/function.mail.php

It is possible that this option is disabled on your server so you should set up sending e-mails using SMTP server.

To set up SMTP details open up file application/config/email.php and set up this:

//set mail sending protocol (mail, sendmail or smtp)
$config['protocol'] = 'smtp';
//sendmail path (applies only if you are using sendmail protocol)
$config['mailpath'] = '/usr/sbin/sendmail';
//smtp settings (applies only if you are using smtp protocol)
$config['smtp_host'] = 'your.mail.hostname';
$config['smtp_port'] = 25;
$config['smtp_user'] = 'your-email-user-name-or-e-mail-address';
$config['smtp_pass'] = 'your-email-account-password';
Setting this will make script send all emails using SMTP server.