When a received email message requests a read receipt, Outlook will prompt you before sending the receipt.
To permanently set Always send a response or Never send a response:
1. Open Outlook.
2. Press Tools on the menu bar, and press Options.
3. Select the General or Preferences tab.
4. Press E-mail Options.
5. Press Tracking Options.
6. At the bottom of this dialog, select Always send a response or Never send a response.
7. Press OK until all dialog boxes are closed.