Synopsis
An open SMTP relay is running on the remote host.
Description
Nessus has detected that the remote SMTP server allows mail relaying.
This issue allows any spammer to use your mail server to send their mail to the world, thus flooding your network bandwidth and possibly getting your mail server blacklisted.
Solution
Reconfigure your SMTP server so that it cannot be used as an indiscriminate SMTP relay. Make sure that the server uses appropriate access controls to limit the extent to which relaying is possible.