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VPOP3 Enterprise has an RBL checking feature which is configured in the VPOP3 Settings at Services → SMTP Server → SPAM Reduction → Realtime Blacklist Rules
If it does not seem to be working properly, there are a few reasons why the RBL feature may not work.
If you go to Settings → Diagnostics, and set 'Log Level' to 'Full Logging', then look in the VPOP3.LOG file after you have had an incoming SMTP message, you should see lines containing with “Test RBL Server <server> <address being looked up> FOUND|NOT FOUND”. Those will show what RBL checks VPOP3 is doing, and what the results were.