Q. How do I clean out my mailbox? Empty the Deleted Items folder – Empty the Deleted Items folder frequently to make sure you are not keeping messages you don’t need. Store attachments outside your mailbox – As attachments accumulate over time, they can take up a lot of space. For attachments, you want to keep, consider saving them to folders on your home drive or shared departmental drive. In Outlook, choose File> Cleanup Tools > Mailbox Cleanup to identify items older than a certain date or larger than a certain size. Consider deleting these.