Author: W B Hacker Date: To: exim users Subject: Re: [exim] Sender verification, permanent vs. transient error codes
Eric Messick wrote: > On 1/25/07, Magnus Holmgren <holmgren@???> wrote:
>>
>> No, I connected (with telnet) to [209.51.152.98]:25, said (after EHLO)
>> MAIL
>> FROM: magnus@??? and RCPT TO: postmaster@(the domain name in the
>> greeting). No error. Now I did the same, but with MAIL FROM:
>> postmaster@???. Again no error.
>
>
> Hmmm.... I should try that while I'm watching packets.
>
> That would tend to support the "got stuck in the bad guy DBM database"
> theory. Why else would some addresses succeed and others fail?
>
> -eric
JFWIW, 'Why else' when you are running Qmail can also include blocking of, for
example, the 'nth' and subsequent attempts at delivery to a destination over
multiple, parallel connections from the same sending server - a Qmail trait of
long-standing.
More smtp-compliant MTA use a single connection to send ONE copy of a message
with ONE set of handshakes and let the receiving server dupicate it locally.
Much more efficient of bandwidth, CPU, & other resources at both ends.
'n' can be as low as 2 for Exim's 'smtp_accept_max_per_host' allowing for a
simultaneous sender-verify, but blocking parallelizing spambots, and forcing
Qmail to 'come back later'. Often more than once.
This does not appear to be your specific situation, but you may encounter it
also, and it might initially look like an unpredictable form of blacklisting.
A side effect, BTW, is that Qmail is slower - *very much* slower - to complete
multiple-recipient-same-server delivery than 'proper' MTA - just the reverse of
their historical claim to fame, and dramatically so.
But if it acts like a spambot, walks like a spambot, and talks like a spambot -
it will have to take the heat.
