Microsoft Outlook Express 4.5

Microsoft Outlook 8.5 and earlier, and Outlook Express 5 and earlier, with the "Automatically put people I reply to in my address book" option enabled, do not notify the user when the "Reply-To" address is different than the "From" address, which could allow an untrusted remote attacker to spoof legitimate addresses and intercept email from the client that is intended for another user.