Outlook for Web (the Mail app in Microsoft 365 online) and Microsoft Outlook all allow you to send Automatic Replies (such as out-of-office messages) to incoming messages. One can also set separate messages from people within OU and people outside of OU. Optionally, set a date range for your automatic replies. This will turn off automatic replies at the date and time you enter for the end time. Otherwise, you'll need to turn off automatic replies manually. For additional information on Automatic Replies, please see the Microsoft help article here.
Outlook for the Web
While logged in at outlook.office.com, click the gear at the upper right, then select View all Outlook settings. While on the Mail tab, select Automatic Replies to set your reply settings and message.
Outlook 365 for Windows (Also Outlook 2016, 2019)
While you have Outlook open, click File. With the Info home tab active, you can now click on the Automatic Replies button to set your reply settings and message. On the Inside My Organization tab, type the response that you want to send to teammates or colleagues while you are out of the office. Note: Sending automatic replies to anyone outside my organization will send your automatic reply to every email, including newsletters, advertisements, and potentially, junk email. If you want to send automatic replies to those outside your organization, we recommend choosing My contacts only. Select OK to save your settings when done.
Outlook 365 for Mac
While you have Outlook open, click the “Tools” menu option. Now select the Automatic Replies option to set your reply settings and message.