If you have a secondary mailbox that you have full permissions to, you can change the Auto-replies for that mailbox.
Open a Browser.
Go to office.com.
Go to Outlook icon on the left.
Once Outlook web version opens, click on profile picture in right hand corner.
Click on Open another mailbox.
Type invoice@lkeeley.com and click Open.
Once the new mailbox loads on screen, click the Settings wheel just to the left of profile icon.
At the bottom of the settings window that opens on the right, click View all Outlook settings.
Click on the Automatic Replies.
Make your changes here and click Save.