Configure Out Of Office Auto Reply for Internet Address In Exchange 2003

In Exchange 2003, by default the Out of Office Assistant only works for the internal senders which is on the same local network. When you try to send an email using external email address or internet email address (eg. gmail.com), you will not receive the auto reply assistant. This are meant for security reasons to prevent spammers to get hold of a valid email address or so that unauthorized people do not know when a user are actually out of the office.
It also depends on your organization whether to allow or not allow this feature. If you know what you are doing, then follow this guide to enable auto response to external email addresses.
To turn on Out of Office replies to external email addresses, follow these steps:

In your Exchange 2003 server, start Exchange System Manager.
Expand Global Settings, select Internet Message Formats.
On the right panel, right click the default SMTP domain and click Properties. The default SMTP domain is “*”.
In Properties windows, click the Advanced tab, and select the Allow out of office responses check box
Restart the SMTP (Simple Mail Transfer Protocol) and Microsoft Exchange Routing Engine services for it to take effect.