Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!LCS.MIT.EDU!sra
From: sra@LCS.MIT.EDU (Rob Austein)
Newsgroups: comp.protocols.tcp-ip
Subject: Host requirements and SMTP
Message-ID: <9001081715.aa24442@mintaka.lcs.mit.edu>
Date: 8 Jan 90 22:15:12 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 18

Julian,

Back when Mark Crispin and I were implementing the current interface
between the TOPS-20 mailer and domain resolver, we concluded that we
would be best off avoiding the IN-ADDR.ARPA portion of the DNS tree if
at all possible.  Informal observation convinced us that the IN-ADDR
tree is, on the whole, significantly less accurate than the main
portion of the DNS tree.  Sad, but true.  So our validation mechanism
does indeed want the name from the HELO command as a starting point.
It will let the mail through if the validation fails, it just makes a
lot of rude comments and flags the failure in the Received: header.

There are other reasons why the HELO command is useful (eg, the BSMTP
protocol), but this one is rooted in a real and current Internet
problem.  I for one would be unhappy if the SMTP protocol didn't have
the HELO command.

--Rob Austein