[exim] flood protection

hello,

imagine a situation when certain spam hosts are flooding exim 4.66 mail server with thousands of email messages per minute.
all of those rcps are rejected because of presence in the gray-lists.

Some questions realated to solving the problem:

is exim able to limit message rate from a certain host?
or...maybe it is possible to give kind of ban on certain ip address depending on spam-list information?

sadly, google seems to give no answers on this problem...

please, share your opinion on this matter, because damn spammers are eating server's bandwidth and hardware resources.

currently i am using exim's log analyzer and firewall deny rule generator, but rule count is increasing in geometrical proggression and server gets to low on resources...

thank you