double check with your host that addressing the SMTP server by IP is valid. The SMTP server may not respond to the IP address.
make sure you are using a valid from address and a valid to address.
make sure the from and address are not the same.
make sure the from address is an address on the same domain as your site.
on the mail server settings tab, you may need to check the option to include the from address as an extra perameter.
if everything is set correctly and the emails are still not coming through, check with the host to see if they can look into the SMTP server error logs to see why the email is not being relayed.