Go to the URL: https://webmail.mun.ca and login with your webmail (Plato, my.mun.ca) Username and Password.
Click on the Filters icon at the bottom of the page.
Click the Vacation icon.
Click Enable Vacation messages box. Type the subject in the next box; type the reason in the next box. Click Save and then you can logout. Please ensure to remove your vacation message when you return.