Turn on or modify automatic replies
Login to https://portal.office.com.
Go to Outlook.
At the top of the Outlook page, select Settings
> View all Outlook settings > Mail > Automatic replies.To turn on automatic replies, select the Turn on automatic replies toggle.
Select the Send replies only during a time period check box if you only want to auto-reply during a certain time, and then enter a start and end time.
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.
Select the check box for any of the following options that you're interested in:
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
In the box, type a message to send to people during the time you're away.
To only send replies to your contacts, select the Send replies only to contacts check box.
Select Save.
To turn off automatic replies, return to the Automatic replies page and select the Automatic replies on toggle.