Exchange allows you to automatically send "Out of Office" notifications to anyone who sends you mail. There are two parts to this.

The first part is creating the server-side rule to be run when you are out of the office. The simple case (which is all that Connector supports) is to have a single rule that sends a simple reply to all "out-of-officeable" messages. (I don't know Exchange's exact rule, but I think it won't send a reply to any message that doesn't include you as an explicit recipient, and it won't send the message more than once to any recipient in any given out-of-office period.)

Connector doesn't currently support creating server-side rules at all, so we handle the out-of-office rule by using OWA's Options page. This is pretty much a kludge, but it works for simple out-of-office messages, and we haven't gotten any bug reports against it yet...

The second part is turning the out-of-office state on or off. This is controlled by a MAPI property on the message store itself, which we can't access via WebDAV. (The message store is not the same as the root folder of the message store.) So again, we use OWA to do this.

Connector (like Outlook) checks the out-of-office state at startup time, and offers to turn it off if it is on.