User Email Quota Notification

The lack of user email quota notification has caused some problems. A couple of months ago, I recieved a message from the system that informed me that the antispam was not going to work on some accounts that had exceeded the soft limit. So I increased the mailbox size. As the past few months have gone by, some peoples email accounts have exploded in size. Increasing the quota is just a bad idea. Setting a hard quota, without a system notification of approaching the limit, will have our phone ringing off the hook. With about 1000 email accounts, this situation is becoming unmanagable.

Is there a way to have a soft quota action for a lower limit, followed by a hard quota action for a higher limit, of rejecting incoming email?

Or perhaps do you have any ideas that might help with the situation?

When people have reached their limit, it would help if we could offer them some sort of email archiving utility. We have not been able to find one that works.