You may want to look at Fail2Ban for this sort of thing… it can monitor your logs and put firewall block in place to stop repeat offenders.
http://www.fail2ban.org/wiki/index.php/Main_Page
--
Merlin Hartley
IT Systems Engineer
MRC Mitochondrial Biology Unit
Cambridge, CB2 0XY
United Kingdom
> On 3 Mar 2016, at 11:21, jarek <jarek@???> wrote:
>
> Hello!
>
> Is it possible, to configure exim, so it will drop/reject message
> processing after first "Unknown user" ?
> One of my servers is under permanent DDOS with thousands of clients
> trying to send messages to non existing recipients.
>
>
> best regards
> Jarek
>
>
> --
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