There was a petition at one point to have the rendering engine changed and Microsoft made some kind of vague promises to improve it. https://freshinbox.com/blog

There was a petition at one point to have the rendering engine changed and Microsoft made some kind of vague promises to improve it. https://freshinbox.com/blog/the-outlook-team-reaches-out/ https://freshinbox.com/blog/the-outlook-team-reaches-out/ I would assume that it's not a simple technical change on their end.