If you check a second Exchange mailbox through your Outlook profile, you cannot set an Out of Office message for that additional mailbox in your Outlook profile. The easiest way to set an Out of Office Message for a second mailbox is to do it through Outlook Web Access.
- Log into Outlook Web Access.
- Click on your name in the top right corner.
- In the Select mailbox box, type the name of the mailbox, and click Open.
- Click on the Options button at the top right corner.
- Click on the Out of Office Assistant link on the left side of the screen.
- Set the out of office message and click Save.