sb: > Our point of view is plain: are we dealing with "proper" e-mail servers?
Good question.
> Our emphasis, therefore, is on the DNS, to identify the sender and
> its MX RR, because it is the de-facto standard to say "this is
> where I receive e-mail".
For the envelope sender address, the sending IP addresses are covered
by SPF policy. Spammers were among the first to adopt it.
> How else could you tell them apart?
Reputation (DNSXL).
Wietse
