Follow the steps below to send automatic (out of office) replies in.Use automatic replies to tell people you won't be responding right away to their email messages.
NOTE: Automatic replies are sent once to each sender.
Step 1. Open Outlook online
Step 2. At the top of the page, select Settings 
then View all Outlook settings then Mail Automatic replies.
Step 3. Toggle on Turn on automatic replies
Step 4. Select the Send replies only during a time period check box, and then enter a start and end time.
NOTE: If you don't set a time period, your automatic reply remains on until you turn it off by selecting the Automatic replies on toggle.
Step 5. Select the check box for any of the following options:
- Block my calendar for this period
- Automatically decline new invitations for events that occur during this period
- Decline and cancel my meetings during this period
Step 6. In the box at the bottom of the window, type a message to send to people during the time you are away.
NOTE: You can use the formatting options at the top of the box to change the font and color of the text or customize your message in other ways.
Step 7. Select the check box for Send replies outside your organization, for senders outside of SSI to get automatic replies,
Step 8. Select Save at the top of the window when compeleted.
NOTE: If you did not set a time period for automatic replies (step 4 earlier), you'll need to turn them off manually. To turn off automatic replies, sign in to Outlook online, choose Settings 
then View full settings then Mail Automatic replies and then toggle the Automatic replies on.