http://oc-co.org/?p=77 (see the link for the text) Conclusion is: if you whitelist 10^4 most frequently interacting MTAs out of assumed total 10^6 MTAs worldwide then you will whitelist 4 out of 6 mails. Whitelist 10^5 m.f.i. MTAs => 5 out of 6 mails will pass without greylisting. 10^3 => 3 out of 6, etc Victor