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From: David Michard on 31 Mar 2010 08:14
Hello,

I guess this message is off-topic as it is only loosely related to postfix.
You may stop reading this now if you are non interested in such topics.

-------
I am responsible for a mailing list with roughly half a million
subscribers. The flow is outgoing only as we send a newsletter to
subscribers.
We implement different techniques to automatically unsubscribe
old/invalid/overquota email addresses, among which postfix VERP seems
to work well.
Our email are emitted from a noreply email address mapped to /dev/null
as we cannot handle individual replies. Information regarding how to
contact us is displayed in every email we send (redirect to a web
form).

Lastly I have been mapping the noreply@ email address to a real
mailbox instead to /dev/null. The results are frightening.
Hundreds of email are sent to the noreply address each day. Some
subscribers hit "reply" to contact us and I can understand that as
most of them are not technically savvy.
The problem is, a lot of replies come from bots / postmasters and so
on : antispam software (please fill this captcha), or worse delivery
failure notifications.
I do not know the applicable RFC by heart but I thought that delivery
failure notification and other automated replies should be sent to the
"return envelope" and not to the "From" field. This is how VERP works
but I now realize that we are missing significant feedback regarding
the validity of our user base as we do not -and cannot- monitor the
noreply email address. We cannot automatically monitor it as we do not
know what kind of email may be sent to the noreply address:
- either a subscriber replies to us, in which case we should
autorespond "please use the web form"
- either an antispam solution asks us to send a confirmation email in
which case we should consider this as a (hard) bounce
- either the reply is a delivery failure notification and we should
consider this as a (hard) bounce
- either the reply is a temporary failure notification and we should
consider this as a (soft) bounce

Therefore we may have email addresses which have been invalid for
months/years but are not detected by our VERP handling software.

I am not willing to develop a software to parse the reply looking for
some magic keywords (such as postmaster, failure...) to do the sorting
as judging by the diversity of the reply that I see this promises to
be an impossible task.
How do mailing-list managers handle this kind of problem using
postfix? Is there a comprehensive database of keywords which can be
implemented to differenciate notifications from other type of emails?

I reckon I am a bit lost on this one :-)
Regards,
David.

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