Embedding base64 images in email - current conditions?

Hey everyone, seeing as you folks are the real email marketing experts here, I just wanted to see if any of you have had experience with embedding base64 images in email. We've recently been experimenting with the <img src="data:image/png;base64,iVBORw0KGgoAA..." /> method, but this technique is still very poorly supported. The more reliable method seems to be editing the multipart content. So...

- Is there a email service provider out there that allows you to edit multipart/mime content?
- Have you succeeded in embedding images using this method?

We'd love to hear your thoughts on this. Note that we still don't think it's a great idea to embed images (for example, two of our test emails went straight to spam in AOL), but it's likely time that we gave our results a refresh. Thanks for helping us!

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