Cloudflare Polish Feature - bug with embeded images in emails

Hi I just wanted to share a quick problem we encountered while using the POLISH feature with cloudflare.

We currently host all our images for our email newsletter on our website. Since upgrading to POLISH the images in our emails seem to be referencing webp images (specifically the PNG ones). You know the odd type of images that have a .png extension but when you look at the image properties are actually webp.

So…
it looks like there are some safeguards to serving webp in HTML email and google, cloudflare, or WHOMEVER is converting the webp embeded PNG’s to jpeg images in gmail.

The result is that our transparent pngs are no longer transparent pngs in our emails.

We disabled the Polish feature and re-uploaded copies of our PNG’s with different filenames and can confirm the issue seems to be based on POLISH, and more particularly cloudflare serving the cached webp images from our server when referenced via html in email.

Can anyone confirm that this would be the case?

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