[exim] connection refused by exim

Hello.

I have debian PC with exim4 relaying a domain that internally is managed by
exchange. This PC with exim is the antispam and antivirus of the domain.

executing
tail -F /var/log/exim4/mainlog

I clearly notice that from internet this exim is being attacked, somebody is
trying to send email to unexistent accounts on this domain.

Please I need to configure exim to allow a maximum of connections per ip on
internet, and at the same time to have a list of valid accounts on the
domain to refuse the emails without send them to the internal server.

te exim is refusing connections from valid servers for this cause.

Thanks in advance for any help, I don't have a big experience with exim

Enediel

Linux user 300141
Debian GNU/Linux