Is there any way to limit this to a sensible amount... Ive had people abusing the mail system so I want to restrict it... Also can anyone think of a sensible amount per account so that it wont mess up my box???

Thankyou this is very important by the way

Sure...on a per-domain basis. Just go to "Tweak Settings" and scroll down to "the maximum each domain can send out per hour" and set it to what you think is appropriate. I have mine set at 1000 but you could set that at a smaller or larger level depending on your usage.

This won't handle it on a per-e-mail account basis, but it should slow down spamming.