The simplest implementation would be a simple 'oracle'. If we were to call the
extension 'XSPF' (for now) and have the grammar:
'XSPF' <SP> (SENDER-HOSTNAME|SENDER_IP) <SP> DOMAIN <SP> LOCALPART
I'm wondering if the SMTP command VRFY could be remodelled to do this
rather than implement a new command. Currently VRFY and EXPN tend to be
disabled in most SMTP servers, since they are typically used to harvest
addresses, and so remain unused. However, the return code would have to
be 252 or something other than 250 or 251.
and reponse of the form:
250 <SP> ('ALLOW'|'DENY') <SP> 'FOR' <SP> TTL-VALUE <SP> 'SECONDS' [<SP> 'FOR
ALL']
The downsides:
4. ESMTP conversations use more bandwidth than DNS over UDP.
But are easier to parse than a DNS response.
--
Anthony C Howe +33 6 11 89 73 78
http://www.snert.com/ ICQ: 7116561 AIM: Sir Wumpus
"...simplicity is a goal of good design,
it is never the starting point." - Dan Geer
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