[exim] delaying inbound messages

I maintain the exim.conf file for the DirectAdmin hosting control panel. One
of our users has suggested we delay all inbound messages on port 25 by three
seconds to help eliminate spam. My thought is that if we're delaying busy
legitimate servers on each delivery, we're not being good neighbors.

He's suggesting this:

<snip>
acl_connect:   
  # Accept right away messages sent on port 587
  accept  hosts = +auth_relay_hosts
          condition = ${if eq {$interface_port}{587} {yes}{no}}  

  # Accept hosts who are polite enough to wait rather than just send, as spammers do
  accept hosts = *
         delay = 3s

  # Deny hosts who don't wait      
  deny message = Too quick on the draw - to unblock wait for helo/ehlo
</snip>

Is there a community concensus on whether or no this is reasonable?

Thanks.

Jeff
--
Jeff Lasman, Nobaloney Internet Services
Post Office Box 52200, Riverside, CA 92517
Our blists address used on lists is for list email only
Phone +1 951 643-5345, or see: http://www.nobaloney.net/contactus.html