Step 1. Log on to portal.office.com with your email address and password
Step 2. Click the square in the top left then click on mail.
Step 3. Click on the cog in the top right to bring up settings and then mail at the bottom
Step 4. Click on automatic replies on the left, then click send automatic replies, set the start time and the end time type out what you want your message to say and then tick the boxes accordingly and then hit save.