I find this *really* annoying

[aluminumsulfate at earthlink.net]

   From: Derek Martin <invalid at pizzashack.org>
   Date: Thu, 7 Apr 2005 15:14:45 -0400

   and block that domain.  Do it by having outgoing mail servers
   cryptographically sign messages with keys registered in DNS, and
   reject mail if the signatures don't match, or if the domain is known
   to mass mail spam.  But DON'T do it by blocking everyone in the known

I'm afraid signing SMTP won't help the spam problem.  Even spammers
have signatures.  :) This would just provide connection-level security
a la IPsec.  There would need to be a "web of trust" with which mail
servers could evaluate the credibility of an incoming message in order
for a crypto solution to work....

One way to get around the problem (and reclaim our rights as emailers)
might be to set up a peer-to-peer network of relays around the
Internet.  Perhaps a "Never Block List" (NBL :) in the DNS could
advertise open relays.  Perhaps publish SRV records for VPN
gateways....  That way, email would be routed through "trusted"
domains.  And, if they *have* to go through a registered relay, you
could have some degree of control over which relay is used....

Of course, spammers could also make use of such routing techniques.
The operative point is that this would essentially render blocking by
IP dynamism useless.  Hopefully, "filtering" services will stop
blocking dynamic IPs when they realize it's futility.