I use Opera as my mail client and it almost never displays images properly, so today when I received a newsletter that was full of images, I checked out its source and found that all of its images had been encoded in base64. I've been aware of the mechanics of the technique for a little while but was under the impression that there were problems with Internet Explorer, so was wondering how common it is for HTML emails to be sent like this and how safe it is to do so? The newsletter I received today certainly looks better than any other I've received in Opera, but I'm wondering if it would be the same for other clients.
It's also something we might not put much effort into supporting because of the advantages of linked images (smaller file size of the email itself, encourages people to allow images which helps open tracking).
But if you'd like to pass the source code on to us via email, we'd be interested in testing if it works better than our previous tests.