> Login to portal.office.com 

> Locate to Outlook.

> Go to the settings cog in the top right hand corner.

> Then go down to 'View all Outlook settings'.

> This pop up box should appear, go down to 'Automatic replies'.

> Once in Automatic replies, it will automatically be turned on, to turn it on toggle the switch to ON.

> Turning on, you can type your Out of Office message into the text box.

> You can also set a start time and an end time, if you would like your Out of Office for certain times.

> By pressing 'Save', if anyone sends you an email then onwards it will send back the Out of Office message you have put.