1.
Determine a suitable timeframe to leave attachments in users sent items…typically 30 to 60 days is sufficient time. This allows users to re-forward previously sent messages with attachments without having to re-attach the file.
2.
Set up an email policy that deletes attachments “sent” by a user.
3.
Set the policy to run weekly off hours prior to a full Exchange backup.
4.
Perform a full backup of your Exchange Server databases
5.
Perform a full backup of the location the files are moved to.