Yes you can limit incoming messages. (Search for "Rate Limiting" in the specification?) However, my experience is that this won't help much if at all. However, It could help prevent servers on your network from spewing spam if they get infected.
I use a number of features for Blocking Spam with Exim. One the the most effective is to inject delays for servers which are not configured correctly. This may cause some problems for automated email systems (airlines, banks, governments, advertisers, etc.), but has little impact on person mail.