Turn on automatic replies in Outlook so people know you're away.
In Outlook on the web, click Settings (gear icon) > Mail > Automatic replies.
Check "Only send during this time range" and pick your start and end dates so replies turn off automatically when you're back.
Keep it short — include when you'll be back and who to contact in your absence. Use the "Outside My Organization" tab to write a separate message for external senders.
In Outlook on the web, hit Save. You'll see a banner confirming automatic replies are on. To turn it off early, go back to the same menu and select "Don't send automatic replies."