Double Irony! (was Re: [linux-elitists] ruben's stupid filter)

Sun Mar 24 21:42:26 PST 2002

On Sun, Mar 24, 2002 at 01:41:30PM -0800, Dan Wilder wrote:
> I'm playing with automating the idea of SMTP blacklisting mail from those 
> who refuse bounces from our mailer-daemon.  Have been doing something

That's easy, I already have this on, it's completely
automated with SMTP callbacks:
moremagic:~$ telnet 25
Connected to
Escape character is '^]'.
220 ESMTP Exim 3.31-VA-mm2 #1 Sun, 24 Mar 2002 21:36:16 -0800 - SF usw-list mm5
helo domain
250 Hello []
mail from: <>
250 <> is syntactically correct
rcpt to:
250 <> is syntactically correct
354 Enter message, ending with "." on a line by itself
550-Envelope sender verification failed
550 rejected: Cannot route to envelope sender <> (The envelope sender does not exist according to your mail server when it was asked): response from [] after "MAIL FROM: <>" was "501 bogus mail from". This does not help fight spam effectively, breaks RFCs, and prevents you from getting bounces so we can't accept mail from you

> This catches, for example, hotmail, which refuses bounces, but which also

That's not true.
Connected to
Escape character is '^]'.
220-HotMail (NO UCE) ESMTP server ready at Sun, 24 Mar 2002 21:38:26 -0800 
220 ESMTP spoken here
ehlo domain Hello
250 SIZE 1572864
mail from: <>
250 Requested mail action okay, completed
rcpt to: <>
250 Requested mail action okay, completed
354 Start mail input; end with <CRLF>.<CRLF>
Subject: test

Do not reply, thank you :-)
250 Requested mail action okay, completed
221 Service closing transmission channel

> Unfortunately the RFCs appear to prohibit validating the actual
> sending host against DNS and then declining mail based on that
> validation.  That'd catch a large part of the spam that comes in.

I don't  see which  RFC forbids one,  and even  if there were  to be  one, I
wouldn't care and do SMTP callbacks anyway.
BTW, for those curious of the checks that does on a piece
of mail, see:

> Aside from RFC considerations, this is not feasible on pragmatic 
> grounds: way too many legitimate hosts with broken DNS.

Do you mean forward and reverse on  the calling host? Yeah, I don't do that,
because it probably catches as much legitimate mail as it catches spam.

But I will not accept an envelope sender that is broken in any way.

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