A user called me to say that he had forgotten to set his out of office message when he went on a weeks leave and that he would not be able to remotely access to set it. He asked if I could set it for him. I advised that I would do so using a feature of OWA on exchange 2010. Signing in as an administator simply select the “Manage” button along the top – select another user from the drop down and then select the user you need to change settings for.
The system will advise that you are operating “on behalf of” the user and that you need to log off when finished. Assuming that you have enable automatic replies at the hub level you can simply turn on automatic replies and select a date and time window for that to be active – along with a message.