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Log into the Outlook Web App at https://outlook.office365.com using your own Office 365 credentials (SMU email address/password)
Click on your profile image (or placeholder image) on the top righ
Choose Open another mailbox
Type in the name or email address of the Shared Mailbox and select it
Click the Cog at the top right of the screen and then click on View all Outlook settings at the bottom
Click Automatic replies configure your automatic reply and you’re done.