Hi, We have a requirement wherein Auto-Reply / Out-Of-Office replies should to allowed out of Exchange Org, for specific users only. Is this possible ?

With exchange 2003 there is no current way to perform this. You can only filter by domain not by user... Do you have any third party content/subject scanning on outbound messages? If so you could allow it all, and drop it at the content scanner with a subject rule.

Content Scanning / Filtering is taken care by our ISP. This requirement is for generic mailboxes such as support@domain.cometc.. wherein external users receive an auto-reply / acknowledgement when they send mails to such mailboxes.