Although untested, here is how I set mine up, can anyone confirm this would work for the OPs question?
anvil_rate_time_unit = 60m smtpd_recipient_limit = 100 smtpd_recipient_overshoot_limit = 20 smtpd_client_message_rate_limit = 100 smtpd_client_recipient_rate_limit = 100 smtpd_client_connection_count_limit = 50
