Are you able to build a plugin for firefox that would work with gmail.
functions of the plug-in:
In gmail there will be a button(plug-in), when you click it, it will send email to the email addresses but add extension at the end of the email.
example if email is being sent to email@[url removed, login to view], when you click button it should send email to email@[url removed, login to view]
Let me know if you are interested