The IE=edge meta tag, placed within the <head></head> of your HTML email, enables CSS3 and media query support on Windows Phones, version 7.5 and higher.
HTML Email Knowledge Base
By default AOL uses it’s own font styling. The fix is very simple and can be overwritten using your own embedded CSS.
If you have set an align attribute in an image to right or left, Thunderbird will add a 3 pixel margin these images.
The accessibility for HTML emails is often overseen, however, with a few tweaks can greatly improve a readers experience using assistive technology.
Just like the Outlook email client, you can target the Windows 10 Mail App using conditional comments.