Open Outlook
Click File
Click Automatic Replies
Select Send automatic replies
Set the date and time range if needed
Type your out of office message
Choose whether to send replies inside your organization
Choose whether to send replies outside your organization
Click OK or Save
Open Outlook on the web
Click Settings
Click View all Outlook settings
Click Mail
Click Automatic replies
Turn on Automatic replies
Type your message
Set the time range if needed
Click Save