Let's look at each in turn.

Relay races
Open SMTP relays are servers that are willing to accept and resend email for anyone. This allows spammers to blast messages to millions of addresses and hide their tracks simultaneously. Many open relays exist across the Internet and spammers search for new ones continuously. Since most open relays are simply the poorly configured SMTP servers of unsuspecting administrators, it is unlikely that this problem will resolve itself.

There is absolutely no valid reason to run an open SMTP relay. Spammers will eventually find it and exploit it. Even if they don't, one of the open relay blacklist testing servers will and your IP range will end up blacklisted across the Internet, unable to send mail to major ISPs and corporations. Imagine explaining that to your boss.

How to be sure you don't have an open relay
In order to setup inbound relay controls, open Domino Administrator, select the Configuration tab, then select Messaging -> Messaging Settings in the left frame. In Messaging settings, select Restrictions and Controls -> SMTP Inbound Controls.

In the "Inbound Relay Controls" section you can allow or deny any domains to which relayed mail may be delivered, as well as, which Internet hosts may connect to this server to relay messages to those domains. The "Inbound Relay Enforcement" section (these are new features in Domino 6) allows you to specify who is exempt from the "Inbound Relay Controls" rules.

Domino 6, by default, denies messages from all hosts to be sent to external internet domains, but only applies this rule to hosts outside the local internet domain. This setting should be secure enough for most organizations.