Sudden increment of storage usage for few hours?

[bhwong]

We install Zimbra 5 to Ubuntu 8 with 120GB of storage. It has been running fine except for a few incidents where our 26GB of free space suddenly drop to about 5GB within an hour and then to recover back to 26GB after about 3-12 hours.

The log files doesn't show anything. What could be the possible cause?

Also, whenever this occur, we will receive few hundreds of disk warning alert from Zimbra! Is there a way to amend the Zimbra alert so that it will only send 1 email per day instead of 1 email every 10 minutes on disk warning?