What is a delegate mailbox?

Delegate Access provides the ability for others to create email messages or respond to meeting requests on your behalf. As the person granting permission, you determine the level of access that the delegate has to your folders. You can grant a delegate permission to read items in your folders or to read, create, change, and delete items. By default, when you add a delegate, the delegate has full access to your Calendar and Tasks folders. The delegate can also respond to meeting requests on your behalf.