Don't they? I thought the recommended retry time was 2 minutes, doubling on each failure, and maxing out at 2 hours.
That's what sendmail does (unless it's retry time has been explicitly set to more than 2 hours, of course). -Philip Richard Frovarp wrote: >I don't think the RFCs specify any time limit. Most timeout after 5 days >of trying. We run 3 equivalent scanning machines, which requires us to >run a greylisting that will sync between them. That could cause a large >delay, if the sending machine tries to send to a different host that >isn't synced. Messages that aren't sent from the same machine (SMTP >farms like at GMail) can cause trouble as well, since the IP will >change. The whitelist usually will timeout after a period of time, so >there is a delay that may be induced again in the future, but that >depends on setup. > >If a sensitive piece of mail needs to get through, it may be possible >for the user to send the message again after the delay period has >elapsed. This would be a new message, but if it leaves the same IP, with >the same from and to pair (or however your greylisting works), it would >fire right on through the greylist no problem. Not a perfect solution, >but should work for rare occasions. > >One probably can whitelist recipients or recipient domains so that they >are not affected by greylisting. > >Last week greylisting stopped 1.3 million messages, which is after the >blacklists and greet pause did their significant work. > >Richard > >
