We are seeing a slight 30-60 second delay on incomming email, which I've tracked down to the DNS blacklist lookups.
Correct.
I have a couple of questions regarding how to fix this, if possible. Granted, I do have 14 rules, which I suppose I could cut back on.
The 14 rules won't cause any noticeable delays. Specifically, they might use a bit of CPU time -- but if they were using 30-60 seconds worth of CPU time, your mailserver wouldn't be able to process much E-mail.
1. Why aren't these queries done in parallel? Could they be? I suspect this would speed them up by a factor of 10.
I'm guessing it was done because it was easier. Remember, Ipswitch wrote the anti-spam piece on their own, without any previous anti-spam expertise.
We originally wrote Declude JunkMail to run the spam tests in serial (ala IMail) because there were only 2 common spam databases at that time (so the delay wasn't noticeable) and to get the product out the door more quickly. Shortly afterwards, we changed the code to run them in parallel, as it is much more efficient that way. At 60 seconds per E-mail, older versions of IMail were limited to about 40,000 E-mails/day that they could process.
2. Is 14 rules too many, or do I just have to live with a 30 delay at this number?
The rules are not the issue. Rules use up very little CPU time.
3. Would caching speed this up? I have the iMail DNS cache set to 200. Does this get used for blacklists? Should I up it?
I would recommend not using their cache -- I don't believe the bugs have been worked out yet. I can't say for certain if it is also used by the blacklists.
Even if it is used by their blacklists, it won't cause a noticeable improvement. Since your local DNS server caches the results, it only saves the round-trip time to your DNS server. Assuming a local DNS server, that's perhaps 5ms at the most per spam database.
4. Has anyone implimented some kind of caching on their local DNS server that would speed this up? We run MS DNS, not sure what the caching is like.
Caching works automatically on DNS servers -- you don't need to do anything special. The problem is that each spam that comes in normally comes from a different IP than ones you have looked up recently, so caching doesn't help there.
-Scott
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