Configuration of a vacation message depends on a mail system which hosts your mailbox (Exchange 2003 or Exchange 2007). You can verify it here
Vacation Message (Exchange 2003)
When you are going on vacation or you are away from CERN for a while, you may want to setup an automatic response which will be sent in reply to mails you willl receive.
This feature is called the Out of Office Assistant.
To configure the Out of Office Assistant, go to either:
MMM Site (http://cern.ch/mmm): Services -> CERN Tools -> Vacation Message.
Outlook Web Access: CERN Tools -> Vacation Message.
Vacation Message (Exchange 2007)
you need to open MMM site(http://cern.ch/mmm) : Mail services -> OWA-Exchange 2007 pilot users ONLY.
Then, when you are inside your mailbox choose: Options -> Out of office Assistant.