Re: [exim] Greylisting - how do you implement?

Marc Perkel wrote:

>
> It doesn't require special whitelisting although you could if you wanted
> to. If the dead IP which is the lowest MX were dead to everyone except a
> white list that you would set with iptables then you could whitelist.
> But it's not really necessary. And technically you don't have to have 3
> IP addresses. All you have to do is point the bogus MX records to any IP
> with port 25 closed.

You really should control the additional IPs if you want to be sure port
25 stays closed. What happens if you point to an IP you don't control
and someone suddently put an SMTP server on this IP and starts answering
5xx errors to all your mails?