The Windows 2008 built in backup is not exchange aware as you may or may not know. This means that whilst you can back up and restore the data on your server, it will not clear your Exchange transaction logs.
To get rid of these logs and to save some disk space, it may be an idea to periodically turn on circular logging to get rid of the log files taking up your valuable disk space. To this, follow the steps below.
Log into the Exchange management console, then in the conolse tree on the left, expand Server Configuration and then click on Mailbox.
In the bottom right pane, right click on the storage group that you wish to modify and choose properties, then tick the box that says Enable circular logging.
To make this change apply, you need to either restart the Microsoft Exchange Information Store service, or mount and dismount the storage group you just modified.
You can then simply go back in and re-tick the option once the logs have gone from the folder containing the transaction logs for that storage group.