My links system is unable to send mail. Can anyone please inform me if the following are correct/incorrect

Links.cfg
----------
# PATH of sendmail.
# $db_mail_path = '';

# SMTP Server
$db_smtp_server = 'nigeria-resources.com';

# Email address of the administrator. BE SURE TO SET!
$db_admin_email = 'admin@nigeria-resources.com';

The error I get after validating a link is:

Error Message : Unable to send addition message. Reason: SMTP: Unspecified communications error.

Any help would be most welcome.