On 27 Apr 2012, at 17:20, kar...@mailcan.com wrote:
Is there any way to prevent Postfix from making those repeated DNS checks, regardless of whether it's externally to Spamhaus' servers, or to a locally cached DNS result?
No. Well you could but it would be futile make-work that adds needless complexity and extra (unwanted?) configuration/management overhead. And the end result will be no better than what you already have. The "cost" of a DNS lookup is frankly not worth worrying about. So don't. :-)
Now in principle you could develop some sort of standalone process and back-end database which remembers RBL answers for a while. But this will almost certainly be SLOWER and less efficient than a DNS lookup. You'd need to invent some sort of API or protocol for adding info to that database and looking it up. And you'd need some way of cleaning out stale entries from that database. This is beginning to smell very much like something the DNS already provides for free.
