Exchange Online (Office 365) Mailbox Delegation.
Using this feature, you can assign the access, send on behalf of, and send as permissions for specific users' mailboxes to the desired users and groups.
- Click the Management tab.
- Select Office 365 Management in the left pane. Then click the Mailbox Delegation located under Mailbox Management.
- Select the desired Office 365 account.
- Select the desired users' mailboxes from the list.
- Click the Configure link located at the right extreme.
- Select the desired actions - send on behalf of, send as and full access, and click the '+' icon located beside the grant this permission to field under each action to select the desired users and groups.
- Click Apply.