thanks for your reply. the reason why I ask is that this setting has more implication than I first thought. I was in the process of setting up a "destination_rate_delay" and wondering why it was not working, but having an destination_recipient_limit of 1 means some settings are per recipient and not per domain... (see
http://www.postfix.org/postconf.5.html# ... ient_limit) so essentially a rate_delay would be mostly useless in throttling emails. maybe setting destination_concurrency_limit would be more suited?