Automatic replies are useful for when you will be out of the office for an extended period of time and need to let anyone sending an email know that you will be unable to respond until a certain date, and who to contact if they need a response soon.
On the View tab, select View settings in new Outlook.
Select Accounts > Automatic Replies.
Select the Turn on automatic replies toggle.
Select Send replies only during a time period, and then enter start and end times.
Under Send automatic replies inside your organization, enter the message to send while you're away. (You can use the formatting options for text alignment, color, and emphasis.)
To set up automatic replies to other people, select Send replies outside your organization, then add a separate message for that audience.
Note: Sending replies outside your organization will send your automatic reply to every email you receive, including newsletters, advertisements, and potentially, junk email. If you want to send automatic replies to those outside your organization, we recommend choosing Send replies only to contacts.
When you're done, select Save.
For additional assistance visit this link: Send automatic replies (out of office) from Outlook - Microsoft Support