If you are using an Exchange account, you can auto reply a specified message for the received emails with setting the Out of Office Assistant while you are away, more specifically:
1. In the Mail view, select the exchange account on the Navigation Pane, and click File > Info > Automatic Replies.
(Note: If your outlook have not connected to an Exchange Server, the Automatic Replies option will not appear.)
2. In the Automatic Replies dialog box, (1) select the Send automatic replies option; (2) check the Only send during this time range option and specify the Start time and End time as you need; (3) type the replying message in the below box. See screenshot:
3. If you need to enable auto-reply for external senders too, please (1) click the Outside My Organization (On) tab; (2) check the Auto-reply to people outside my organization option; (3) type the auto replying message in the below box. See screenshot:
4. Click OK to activate the out of office message.