How are you looking to point users to the Flash file? I don't know the most recent stats on Flash visibility through email clients but I remember in the past the argument was against sending a pure Flash file through email. Instead the suggestion was to code an image to link to your page where the Flash movie is located. That's been the practice in my experience, although it was less an issue of ensuring the Flash loaded correctly and more concerned with click conversion and driving donations.
The file size question is a difficult one. I'm spoiled with broadband but I know even at others' homes with lower level cable or DSL service that sites like YouTube still function...with longer load time. My thought would be to prominently place a status/loading bar for those who might be on a slower connection so they know the content is coming and determine what you can do with 1.5 to 2.0 MB.
That seems large by comparison to the numbers in your question but it depends on the graphics, music and length of what you're sending. I'm curious to experience others have in this area.
I agree with Nathan - you do not want flash in your HTML email. You can have the HTML email look like the start of a movie.. or whatever graphics you want in there.. but when clicked - the user should be taken to a web site where a full web browser can load the flash movie.
Re: file size.. users will wait if there is value - but in general it should load as quickly as possible. Looking at your google analytics reports will give you an idea of what percent of visitors come to your site with a fast connection.
Agreed, do not embed the Flash in the email, you will not get the results you want at all because there is no way to control or predict just how all the different email platforms will interpret it, not to mention it getting filtered, tagged, or blocked as a security threat. I for one wouldn't even open it if I saw a flash file attached. Trash, directly, do not pass Go, do not collect $200. Take a screenshot, make it look like a video player or something, and when the user clicks on it, have them go to a landing page. Email is not a multimedia platform, and it's barely even a good platform for HTML (IMO), so make it ridiculously simple.
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