Click on the icon in the top right of your browser Please ensure that this feature is set to off.
Select "Open Another Mailbox" from the drop-down list:
Type in the mailbox you wish to update the OOO for into the pop-out box:
When the Shared Mailbox emails load, click on the cog in the top right and select "Mail" from the drop-down list:
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.