All I can tell you is that Flash is only readable in certain e-mail browsers. Any Flash e-mail that you have received probably only resembles Flash, but is likely a Java application. There are companies that can do this for you.
Supposedly, this issue will be less of an issue in the future, but it doesn't work now.
Thank you Syrinia for your response. The email that I received did contain a flash banner (I created it and embedded it myself in the email message) and it was readable in Netscape Messenger. I can write Java Applets myself but prefer Flash files.