[SAtalk] OT- "greylisting" - opinions from the SA community?

[Ryan Bingham]

I apologize to anyone if this has been brought up before, but I'd be curious to get some opinions on the concept of "greylisting" as a spamfighting tool.  To summarize, it involves initially rejecting an SMTP session from an unknown source in the expection that a valid SMTP host will try again a short time later while a spamming host will not.   Here's a link to a fuller treatment:   http://projects.puremagic.com/greylisting/   Ryan