Active Spam Killer

Maybe your eMail client isn't displaying the message properly, or the message has malformed headers (e.g., MIME type set to something different from the actual content).

If you can get a raw view of the message, then you'll have a better chance of seeing what's really going on (under the hood). Pegasus Mail has a "Raw view" mode which shows everything, unedited. ThunderBird comes close by showing all headers, but it's no replacement for the raw view. Good luck if you're using MS-OutLook (Microsoft seems to be trying to slowly get rid of users' options to see what's going on under the hood).