There's a blog post here from a few years back regarding PNG support: (http://www.campaignmonitor.com/blog/post/2695/lotus-notes-doesnt-support-png-images/)
While obviously Lotus notes versions with issues are pretty scarce now, I know Outlook has gone backwards when it comes to general rendering...and your design guide still recommends avoiding them, but on the basis of Lotus Notes problems.
I've tried looking for info on this elsewhere, but everyone seems to link back to this blog post as the definitive source of info on PNG in html email - so can I suggest it's time for a 2012 update?
What is the state of play in PNG support and particularly when it comes to transparency?
Hi benz, that's a good call - it's probably about time we revisited PNGs in email. We don't seem to get that many reports of issues in email clients these days, so I'd imagine support of PNGs (and transparency) is fairly good, now Lotus Notes is less of a concern. But I'd say keep an eye on the blog - we should have something up there on the topic in the coming month or so :)