On Wed, Jan 6, 2010 at 10:17 AM, Jay Daley
Whenever this comes up, someone mentions Greylisting. Greylisting delays are usually in the minutes; one assumes that by the time it's posted to NZNOG, the delays have become more noticable than that.[1]
I don't think greylisting is well enough standardised to be able to say that. I've certainly seen it set at over an hour by default (though I can't remember where for now).
As someone involved in running a mail server that uses greylisting the biggest issue seems to be other sending mail servers treating our 450 error as a permament failure rather than a temporary failure. The problem seems to stem from some kind of older Microsoft mail servers and maybe some others. From memory this comes from an early RFC (821?) that suggests that mail servers _should_ try delivery again on a temporary failure rather than they must try delivery again. I get involved in almost weekly discussions with mail admins stating that we're rejecting all of their emails when it generally turns out that their mail server is just not following the rules. Cheers Dave