Points of rejection

     With respect to the issue of rejecting before or after DATA, here's a
purely hypothetical suggestion: how about adding a new SMTP command for
transmitting just the message headers?  Something like (vastly simplified):

<<< MAIL FROM:<valid(_at_)spf(_dot_)address>
  >>> 250 OK
<<< RCPT TO:<poor(_at_)victim>
  >>> 250 OK
<<< HDRS
  >>> 354 Go ahead
<<< From: faked(_at_)address
<<< To: poor(_at_)victim
<<< <CRLF>
  >>> 554 Go away, loser

     This ought to resolve the complaints about bandwidth, and help to
delineate "header processing" versus "body processing", which would
undoubtedly be helpful to MTAs.  This could be merged with
SUBMITTER/RFROM/etc. to either use the relevant headers in HDRS or drop
such headers entirely, without incurring nearly as much resource usage as
when everything is stuffed into DATA.

     I do realize that the possibility of actually making such a
fundamental change to SMTP is somewhere on the far side of impossible, but
as a hypothetical suggestion, what do people think?

  --Andrew Church
    achurch(_at_)achurch(_dot_)org
    http://achurch.org/