Don't blame greylisting for this behavior.
Queue-and-retry was an option but it is mandatory since RFC-2821.
The very obsolete RFC-821 stated that "clients should retry".
In the old RFC-2119 it was explained that "should" means recommended.
The actual RFC-2821 states clearly that:
- "the SMTP client retains responsibility for delivery of the message"
- "the SMTP client is encouraged to try again"
- "mail that cannot be transmitted immediately MUST be queued and
periodically retried by the sender."
You'd rather blame the lazy programmers who don't cares about RFCs and other
standards !
Daniele
Tonnerre Lombard wrote:
> The problem is that your users go to web sites and subscribe their mail
> addresses to newsletters generated by PHP programmers. As expected, a
> lot of these try to deliver the mail directly to the destination host
> from the PHP script using some Pear SMTP crap module, rather than local
> sendmail. A typical dialog looks about like this:
>
> Out: 220 planck.ngas.ch ESMTP Postfix (2.5.1)
> In: HELO gmail.com
> Out: 250 planck.ngas.ch
> In: MAIL FROM: <[EMAIL PROTECTED]>
> Out: 250 2.1.0 Ok
> In: RCPT TO: <[EMAIL PROTECTED]>
> Out: 450 4.7.0 You are greylisted for 300 seconds
> In: DATA
> Out: 554 Error: No valid recipients
> In: From [EMAIL PROTECTED]
> Out: 221 2.0.0 error: I can break rules, too. goodbye.
>
> Not very problematic for the mail server but of course the PHP script
> does _not_ attempt redelivery. And your users go to gmail, because
> there they get the mail. Not sure that's desirable for you.
>
> That's the problem I am seeing with Greylisting, and I have discovered
> that methods like rejecting SPAM after DATA can be way more effective
> if the SPAM filter databases are sufficiently trained and the RBLs well
> chosen.
>
> Tonnerre
>
>
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