[Mimedefang] Re: Justifying greylisting to management

Tomasz Ostrowski tometzky at batory.org.pl
Fri Mar 3 04:08:59 EST 2006


On Wed, 01 Mar 2006, David F. Skoll wrote:

> Sendmail has every reason to assume that if an SMTP client has a
> broken implementation of the state machine on one message attempt,
> it probably will break on every attempt, so why tempfail?

This assumption would be wrong. This could be true if there were not
temporary failure on "rcpt" before - then every other attempt would
indeed be the same so there's no reason to bother with 4xx. But if
there's temporary failure then it should be assumed that the
conditions can change and next time there'll be no reason to
tempfail.

RFC2821:
	A rule of thumb to determine whether a reply fits into the
	4yz or the 5yz category (see below) is that replies are 4yz
	if they can be successful if repeated without any change in
	command form or in properties of the sender or receiver (that
	is, the command is repeated identically and the receiver does
	not put up a new implementation.)

In this case if commands are "repeated identically" then they can be
successful, hence proposed 4xx response.

I'm going to send a feature request to
<sendmail-YYYY at support.sendmail.org>.

> True; if bandwidth is a scarce resource, this could be an issue. It
> isn't for us, and I suspect it isn't for most people -- I doubt
> e-mail uses the majority of bandwidth at most organizations.

You're right. Although e-mail is often misused for file transfer -
"ooh, a cool mpeg, let's e-mail it to all my friends".

Pozdrawiam
Tometzky
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