Configure DNS Blacklists (DNSBL) to drop connections from known spam hosts before they enter the network.
Instead of individual sender addresses, use domain-level blocking or keyword filtering (e.g., *@bad-spam-domain.com ) to stay within rule limits.
Enable SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) on Domino 12+ servers to identify and move untrusted mail to users' Junk folders.
For more information, you can find detailed documentation on HCL Product Documentation and HCL Notes and Domino Wiki . If you'd like, I can: