We are seeing a slight 30-60 second delay on incomming email, which I've tracked down to the DNS blacklist lookups. 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.
This is a critical weakness of linking mail flow to external servers. If one of the RBLs is down (it happens frequently, mailpolice was down a couple weeks ago), then each msg will be delayed many 10s of seconds waiting for the RBL query to timeout.
1. Why aren't these queries done in parallel? Could they be? I suspect this would speed them up by a factor of 10.
this is how it is done on IMGate.
2. Is 14 rules too many, or do I just have to live with a 30 delay at this number?
msgs pass through an IMGate server in (policies (including RBL), receive, queue, relay out) in 5 or 6 seconds total. but if one RBL is down, 84 seconds IMGate delay for every msg, mail throughput plummets, and inbound SMTPD processes are quickly at risk of exhaustion.
3. Would caching speed this up?
If the same IP or RHS is attacking you, then your DNS will cache both positive and negative answers, which it should provide in under 1 ms from cache.
4. Has anyone implimented some kind of caching on their local DNS server that would speed this up?
any recursive serious DNS server will cache. I admin an MX whose DNS on the MX is averaging nearly 105 MB of cache.
I know a 30-60 second delay is not that bad
it's a disastrous problem, fix it.
; email is not IM after all. However, prior to having spam filtering, it was virtually instantaneous (1-2 seconds).
this is normal processing delay. shoot for it.
The clients are givin us a hard time about it
... so it sounds like a bad "solution".
even though they love the spam filtering.
who doesn't?
Len
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