Office 365 (Outlook on the web) - Automatic Replies
This topic shows you how to use the Automatic Replies tab. Use automatic replies whenever you want to let people who send you email know that you won't be responding to their messages right away. After automatic replies are turned on, they'll be sent once to each sender.
Note for administrators: Some administrative functions in Office 365 require administrators to access a user's account via Outlook on the web, which requires the user to grant the administrator full mailbox permissions. Once the administrator has full mailbox permissions, they can follow these instructions to access the user's account.
Manage Automatic Replies
To turn on or modify automatic replies, review Microsoft instructions.