Delegates can receive and respond to email messages on your behalf as well as create and edit meeting requests. If full access permissions and Send on Behalf permissions are granted to a mailbox, delegates are able to send mail as the account owner. A delegate can have additional permissions to read, create, and change items in Office 365 mail.
Note: The person who is sharing a mailbox must grant you Folder Visible permission on the root folder of the Exchange mailbox.