[exim] How to throttle SMTP connections from specific hosts

Hi all, forgive me for only including the first question in my subject line:

Question 1:
I need help on throttling connections from a specific host. I want to allow
only 4 SMTP connections from this host at a time.

Question 2:
Also, how can I progressively delay allowed connections from hosts that
connect and attempt delivery to non-existent accounts on my? For example one
host is connecting multiple times and sending to randomly generated
local_parts like:

47a94794.5000202@??? and
4506b291.5060201@???

Which is definitely a spammer behavior.

I would like to progressively delay connections like these so that for each
delivery attempt to a non-existent account the delay before I accept a new
SMTP connection from this hos will be doubled.

Regards,
Eric Kiara