Allow Mailbox Access in Exchange 2010

Use the EMC to grant Full Access permission for a mailbox :

1. In the console tree, navigate to Recipient Configuration > Mailbox.
2. In the result pane, select the mailbox for which you want to grant Full Access permission.
3. In the action pane, under the mailbox name, click Manage Full Access Permission. The Manage Full Access Permission wizard opens.
4. On the Manage Full Access Permission page, click Add.
5. In Select User or Group, select the user to which you want to grant Full Access permission, and then click OK.
6. Click Manage.
7. On the Completion page, the Summary states whether Full Access permission was successfully granted. The summary also displays the Shell command used to grant Full Access permission.
8. Click Finish.

Use the Shell to grant Full Access permission for a mailbox :

Add-MailboxPermission "User A" -User "User B" -AccessRights FullAccess

Use the Shell to grant Receive As permission for a mailbox database :

Add-ADPermission -Identity "DB" -User "User A" -ExtendedRights Receive-As

* You can't use the EMC to grant Receive As permission for a mailbox database.