We have a client that is a non-profit, and, due to a lack of funds, is still running Exchange 5.0 SP2. It is my understanding that you cannot shut off mail relay on that product. Is that true? Are there any third-party products, utilities or reg hacks that will block the ability of outsiders to relay through the server?
That is not true. Sort of. While Exchange 5.0 provides minimal (and I mean minimal) control over incoming e-mail, it does provide some control. Specifically, you can have Exchange 5.0 validate a FROM address when receiving e-mail by entering a registry key on the Exchange server and providing it with a list of addresses.
You can find step-by-step instructions for doing this in Microsoft Knowledge Base article 155683, XFOR: Verification of FROM Address in SMTP Messages.
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