You can have the Internet Agent reject messages from unidentified sources. The Internet Agent will refuse messages from a host if a DNS reverse lookup shows that a "PTR" record does not exist for the IP address of the sender's host.
If you choose not to have the Internet Agent reject messages from unidentified hosts, it will accept messages from any host, but it will display a warning if the sender's host is not authentic.
To configure the Internet Agent to reject messages from unidentified hosts:
In ConsoleOne, right-click the Internet Agent object, then click Properties.
Click SMTP/MIME > Security Settings to display the Security Settings page.
Turn on the Reject Mail if Sender's Identity Cannot Be Verified option.
This setting corresponds with the Internet Agent's /rejbs switch.
Click OK to save your changes.