Step 1: Sign into your Office admin account via https://portal.office.com
Step 2: Navigate to Exchange admin center.
Step 3: On the left pane, click Mail flow >> Remote domains.
Step 4: Click on add a remote domain button on the top-left.
Step 5: Enter a name and the remote domain name and click Next.
Step 6: Select the none radio button and uncheck the Allow automatic replies checkbox.
Step 7: Click Next until the review page and click Save.