Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsd!ogicse!blake!Tomobiki-Cho!mrc
From: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Host requirements and SMTP
Message-ID: <5259@blake.acs.washington.edu>
Date: 8 Jan 90 22:18:59 GMT
References: <9001060622.AA28788@ucbvax.Berkeley.EDU>
Sender: news@blake.acs.washington.edu
Organization: Mendou Zaibatsu, Tomobiki-Cho, Butsumetsu-Shi
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In article <9001060622.AA28788@ucbvax.Berkeley.EDU> CSYSMAS@OAC.UCLA.EDU (Michael Stein) writes:
>HRRFC 5.2.5 says "However, the receiver MUST NOT refuse to accept
>a message, even if the sender's HELO command fails verification."

This brings up a related issue.  The TOPS-20 SMTP server will reject a
HELO under two circumstances:
 a) syntax invalidity
 b) the HELO claims to be the local host, but the IP address is not
    one of the known local IP addresses.

It also requires the successful negotiation of a HELO before starting
a MAIL transaction.

As I read the HRRFC, this is not allowed behavior any more, but I
haven't heard any complaints about this behavior either.  That is, I
have never heard any complaints of mail not getting through to a
TOPS-20 system because the SMTP client:
 a) uses bogus syntax in its HELO
 b) claims to be the TOPS-20 system it is talking to.
 c) doesn't want to do a HELO before starting a transaction

My question is, do we really want to outlaw behavior that isn't
causing a problem?  I can get rid of these behaviors; it involves the
deletion of a few lines of code.  I don't believe it's desirable to do
so.  However, I have this nightmare of someone with a truly sick SMTP
client taking me to task for not obeying the HRRFC.

The check for local host is a useful behavior, albeit less useful in
TCP days.  Basically, it catches "mirrors" (which is what HELO was put
in to get rid of).  Mirrors were a common problem in NCP days, but
still pop up from time to time in TCP.  I've seen hosts in debugging
states that reflect TCP connections.

My understanding of what the HRRFC was trying to outlaw was rejecting
a HELO when the name was unknown, or the name didn't match; problems
that generally were due to out of date host tables or DNS information.
Has the HRRFC gone a bit too far in the opposite direction?
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