Alot of spam is sent by spammers making use of open relay smtp servers. Why any smtp server is open for all routing I am not sure. Here is how you disable it in Lotus Notes and one way of testing it.

Go to Server Configurations in Your Domino Administrator.

Go to the Router/SMTP tab, then the Restrictions and Controls Tab, then the SMTP Inbound Restrictions Tab.

In the Inbound and Relay Controls section, put an asterisk (*) in the "Deny messages from external internet domains" and in the "Deny messages from the following external internet hosts" field to deny all external messages.

You can test it by going here:

http://www.abuse.net/relay.html      NB  If this link changes or fails let me know.

Register first and then you will receive the test email if it is open.

The website might say that server is open, but Notes actually doesn't send the email if it is properly set up. Register first to make sure of this. If you try it anonymously, you have to wait an hour or 2 before you can try again properly.

Another place to test is:  http://www.ordb.com