Your trying to roll a boulder uphill, and it's a big hill & boulder!
Here is your problem, everytime a user gets a new mail or calendar entry it touches the file, which causes the file to be backed up nightly. Depending upon how much mail a user gets this could be becasue of 1 message or hundreds. So, using regular backup/restore methods in tsm causes you to backup all the files which are touched nightly.
However, if you have the TDP for domino you could do your backups with much greater granulatity. However, this requires that domino have logging turned on and a few other configuration changes which you may or may not want to turn on. Refer to the docs and redbooks for further details.
The choice is yours, here at my place we just backup the whole files nightly, and be done with it.
Hope that helps,
Andy.
