I know PNGs are pretty much supported across most browsers if not all at this point.
Are Animated PNG or APNG supported if PNG is supported or are they separate?
Do e-mail programs have the same support?
I was about to post PNG are cannot be animated but then a quick search ... argh!
The page seems to kind of work in Firefox and Opera, but it's not very informative and seems in a sort of experimental state still. Then animations are not the most exciting I have seen either, we have pretty cool animated .gif lying around the web after all these years of practicing with a limited format. This png, I hope the animation is just a bad example because I was expecting more.
It doesn't work in standard Chrome, Safari or IE either.
Anyhow, it seems we have yet to see throbbing/pulsating .png laden web pages yet.
So I figure it may be a while until any mail clients support APNG. Unless Google jumps in, you know how they always surprise us with all the cool stuff.