Re: [exim] How to send bounce messages just after error

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Author: Marco Wessel
To: exim-users
Subject: Re: [exim] How to send bounce messages just after error
On Mar 5, 2007, at 11:46 AM, lista_exim@??? wrote:

> Hi!
> When I receive a message to an false user of my system, I want to
> send a
> bounce message to the original sender just after the error, and I
> don't
> want Exim send the original message to the queue.

I used to do that because my incoming mx was only a frontend,
accepting all users for my domains and then trying to send them
onwards. It was a Bad Idea [tm]. (Rather, it was something I hadn't
thought about yet). It makes your queue fill up faster than a woman's
shopping cart in a discount store. At one point I had over 20000
(yes, twenty thousand) undeliverable bounces. Why? Because most spams
are sent with forged non-existent recipient addresses, and the
remainder is sent using forged recipient addresses that do exist. So
in essence:

- You send lots of people bounces who never sent you an e-mail in the
first place (forged existing recipient addresses)
- Your queue fills up with frozen messages because of all the bounces
that couldn't be delivered. (forged non-existent recipient addresses).

I now reject unknown sender addresses at MAIL time, and unknown
recipients at RCPT time. The only mails getting stuck on my queue now
are mails from locally submitted clients.

You really, really want to reject at RCPT time.