1. Browse to https://mail.office365.com and log in as yourself

  2. Click on the icon in the top right of your browser
    Please ensure that this feature is set to off.

  3. Select "Open Another Mailbox" from the drop-down list:
  4. Type in the mailbox you wish to update the OOO for into the pop-out box:
  5. When the Shared Mailbox emails load, click on the cog in the top right and select "Mail" from the drop-down list:
  6. On the left-side of your browser should appear an options menu; browse to "Automatic Replies", turn on "Send automatic replies" and type your replies in the boxes provided. Ensure you complete the boxes for both Internal and External customers.