throttle 3rd party email instead of reject.(Incoming)

We have multiple 3rd parties that send email to our server, We have implemented quota by entering the limit in policyd throttle table. I believe if they hit the limit it will stop receiving and send's them a msg.

I would like to do similar on what google, hotmail does were it reject and ask you try again later, instead of just rejecting.

Any ideas on what I should be looking at?

Thanks