Re: [Exim] SPF

Someone in a mail list once outlined a pretty simple way to protect
against some UCE. Instead of a PUSH mail system like we have now, we
would have a PULL system. In other words, (this is somewhat simplified
and may not be complete), server A contacts server B and says I have
mail for you and gives a receipt number. Server B then looks up the
host presented in the HELO in the public DNS system, and calls it back
and asks if there is any mail matching a given receipt number.

Chad