If you encounter low disk space issues, you can perform the following actions to correct the issue: Exchange 2010

If you encounter low disk space issues, you can perform the following actions to correct the issue:

• Delete content from mailboxes. Specifically, you can delete messages from the Deleted Items and Sent Items folders.
• Purge items from the Recoverable Items folder. For details, see Clean Up the Recoverable Items Folder.
• Run database maintenance. For details, see Maintain Mailbox Databases.
• Purge transaction logs. For details, see Understanding High Availability Factors.
• Enable circular logging. For details, see Configure Mailbox Database Properties.
• Change the database path to a hard disk drive that has more space. For details, see Move the Mailbox Database Path for a Mailbox Database Copy.

from : https://technet.microsoft.com/en-us/library/bb331958(v=exchg.141).aspx