Out of Office Assistant not working.

If you use the Out Of Office Assistant and turn on the out-of-office reply, the internal senders (on the local network) receive the automatic reply message, but external senders (on the Internet) may not receive the automatic reply.

CAUSE

By default, the out-of-office reply to Internet recipients is turned off.

RESOLUTION
To turn on out-of-office replies to the Internet, follow these steps:
On the Exchange server, start Exchange System Manager.
Double-click Global Settings, and then click Internet Message Formats.
In the Details pane, right-click the Domain name, and then click Properties. The default SMTP domain is “*”.