Best method to throttle mail to one user

[jeffs]

I have a postfix system set up that works fine (well, maybe that is 
because it is not totally on-line yet :-\ ).  But testing has been great.

Once it goes live this system is going to be used to send email alerts 
to users based on certain database activity.  Actually, a script which 
runs against user names and email addresses in the database will be 
kicking off the alerts.  This is not a system that uses postfix for 
general email type of activity -- it will be used only for outbound 
alerts.   I've got that  part to work already just fine.

There is the slight potential for abuse by these logged in users that 
one or two may figure out a way to send spam through this system by 
forging (not login) credentials that the database uses to sort out 
outbound email.

In this particular system if spam is going to go out via the method 
mentioned above, it will always be destined for one particular user, 
although those users will change over time and it is not feasible to 
predetermine which user may be on the receiving end.

What would be the best method in postfix to shut down or stop a sudden 
flurry of emails to one user.  It will always be a sudden jump in 
outbound emails since typical outbound alerts will not happen that often.

Thanks in advance.