Is JavaScript supported in an email message?
http://en.wikipedia.org/wiki/Comparison_of_e-mail_clients
Old clients, such as Lotus Notes, Mozilla Thunderbird, Outlook Express, and Windows Live Mail all seem to have supported some sort of JavaScript execution. Nothing else does.
It seems like a bad idea security-wise, so I would expect this to be a feature that won't always be around, even in these clients.
You aren't going to get executable JavaScript onto a server and into a mail client. But emails DO support links, you can always link to your content within an email.
For most mail clients, no.
It may be, but mail clients won't read it & mail servers may reject it. So leave it out.