We have already covered setting up of Out of Office replies in Outlook 2010. Similarly if you want to setup Out of Office replies in Outlook Web Apps then you can do the following
In Outlook Web Apps Home page, click on the Options link available under Outlook section.
Then click on the Tell people you’re on vacation link under the Shortcuts section available on the right sidebar. This would display the following Automatic Replies section. You can also go to the Automatic Replies section through Organize Email –> Automatic Replies.
To setup Out of Office message, select Send automatic replies radio option. And by marking the check box Send replies only during this time period you can define the specific period for which Out of Office messages needs to be sent. Now type the Out of Office message in the rich text area. This would enable the Out Of Office replies for the senders within your organization. If you want to enable for senders outside your organization then mark the check box with label as Send automatic reply messages to senders outside my organization. It is recommended to select Send replies only to senders in my Contacts list radio option as this would avoid replying to any junk emails received from spammers.
You can use the same message text that was used for senders of your organization. After making the necessary changes, click on the Save link at the save at the bottom of Automatic Replies screen.