I found this info in a previous post on this forum:

I wanted to know if anyone had any luck in creating an email signature with a
flash file without using the stationary feature and making it available and
viewable in most online and offline email servers.

most email providers (especially web mail) will prevent the flash files from
loading as they can do all sorts of interesting things like reporting back to
the server when the email is viewed.

I've been working on trying to create a flash signature embedded in a html
file within a web archive. The flash embed links to a .swf on our server and
has worked to mixed results. The flash signature has appeared within an email
received in the Mail.app in OS X, however, the buttons within the flash
doent don't work. It has not appeared on several online mail services,
including G-mail, however, has appeared through the .mac mail service working
100% as intended. The flash signature contains two links, one to open up the
user's email program with ours in the "to" input, the other link to our website.

I was wondering if any attempts have been made or if it's even possible to
export from flash as a .mov quicktime and use the quicktime in a signature
instead, linking the user to a quicktime .mov file on our server. I've taken
initial attempts at this, without much luck. The signature appears fine within
the mail app, but again, the button links don't respond. I suppose this
doesn't change the fact, on the whole, that the email would still be required
to view HTML in order to see the quicktime. Please, any help or suggestions
are much appreciated by all. Thank you.