I've got an application that sends out notification emails to users of the application (this is not spam; the information in these emails is solicited and useful, and is also a feature turned off by default and must be enabled by the user). The app is still in beta, and one of our testers reports that the notification emails are going to his junk mail folder in Outlook 2003. This is the only reported case of this, but I asked him to send me the email headers from the message, and I noticed that there is a header there labeled "X-CAA-SPAM" with a value of 00000 .

I'm a programmer, so I'm fairly green in the world of successful automated emails - does anyone know if this header is the culprit? If not, any suggestions?