Online Version
 

Click the settings gear icon in the top right corner.

Go to account --> Automatic replies --> Turn on automatic replies
 

After you turn on automatic replies, you can specify a time and date range.

If you don't select the "Send replies only during a time period" automatic replies will be sent until you turn it off manually. 

After turning on automatic replies, you can type your message into the text box.

Outlook App (Windows)

Go to the File tab in the top left.

Click the Automatic Replies button.



Follow the instructions above to set up an automatic reply. 

Outlook App (Macbook)

In the Mac toolbar, click on Tools --> Automatic Replies.

Follow the instructions above to set up an automatic reply.