SMTP Relay 550 5.7.1. Error

The server rejected one or more recipient addresses. The server response was: 550 5.7.1 Unable to relay

1. Open Control panel
2. Open Administrative tool
3. Open Internet information service
4. Right click on your “Default SMTP Virtual Server”.
5. Properties -> Access -> Relay Restrictions.
6. Grant access to the local host at address 127.0.0.1 or Your "IP Address"
7. Retain the "Only the list below" setting.