I have to ask everyones opinion. I’m at an assigmnet that has 20 DNSBL sites the Domino server looks up to, obviously for each email. Is this too many? I would think that about 5 should be enough. Performance issues with too many look ups?
Your advice is appreciated.
Subject: How many DNSBL sites?
Before I implemented a separate spam filter I used five DNSBL sites and there was no noticeable performance issue. With 20 you’re probably going to notice a latency as the server does up to 20 lookups for every piece of incoming SMTP mail. If someone is using 20 DNSBL sites they really should consider using an external spam filter to offload the processing from the mail server.