There are two types of permissions you can apply through the Cobweb Control Panel:
Full Access Permissions
Full Access gives a user full visibility of another mailbox, including the ability to edit or delete items.
When you have Full Access permissions and use Outlook for Windows, Outlook will attempt to automatically add the other mailbox as an additional mailbox.
Full Access does not allow a user to send as another user. These permissions must be applied separately.
Send on Behalf/Send as Permissions
Send As allows a user to send as another. An email sent this way will appear to have been sent as the other user. e.g. If User A sends as User B, the recipient will only see the sender as User B.
Send of Behalf allows a user to send as another, but it will show the the original user as having sent it. e.g. If user A sends on behalf of User B, the recipient will see it comes from User A on behalf of User B.
Full access permissions