limiting emails sent per hour

I have set a limit of 500 emails a domain can send in an hour. What I noticed is that a customer was sending 100 emails in an hour from his domain in an hour and each email had around 100 recipients. Does it mean 100 emails in an hour or 10,000 emails in an hour. If it is considered 10,000 emails per hour, then what is no immediate delivery: more than 10 messages received in one connection? If it is 100 emails per hour, I want to know why his emails were being rejected as he was getting a bounce stating the domain has already reached the limit (500 emails in an hour.) Secondly, there is another domain which is sending mass emails from the server. It already has around 3,000 + emails in the queue and the I have counted up to 750 emails sent by the domain in the last hour. All the emails are still in the queue. The log for the domain again says no immediate delivery: more than 10 messages received in one connection. I am very much confused with the rate limit stuff in WHM. Can anybody guide me?

 

There is no limit set and the default limit in exim is 10 per connection.

 

Can anybody tell me how to find out how many emails a domain has sent in a specific interval so that I can prove to the customer that he is indeed sending more than the limit set in the server and hence the emails are bouncing?