The Holiday Reply / Vacation Notice is available via the Main Menu and Settings.
The Vacation Notice is simply a preset Filter rule. You'll see a link to Filter Rules also in the left side panel.
You enable the Vacation Notice via the Enable tick box. Set up the time period and frequency of notices sent in reply to individual senders and of course your personalised message.
Hi Hamlie, it looks like Gondola has got you sorted. Please remember to like the post if it's helpful. I've marked it as best answer for you.