
This way Yahoo! will ignore the query entirely. Since Yahoo! also does not support attribute selectors, you can use them within your media queries. On top of that, it gets confused with your first declaration which is therefore ignored. It then renders each of the styles as if they are outside of the media query to begin with. Yahoo! ignores your media query declaration along with all of its conditional statements. This means that the new font and font size was applicable only to the email message that you were composing. Up until now, the Mail app allowed us to change the font and font size only while composing an email. Read more at Yahoo! Mail Now Supports Media Queries. For instance, I like the Palatino Linotype font and set it as the default font in Word, Evernote, and other frequently used applications. As of March 2015, Yahoo! Mail has remedied its issue with media query rendering. So it’s a good habit to place your styles in both locations. This client also converts your body to a div, however, it still retains it’s attributes as long as they are supported within a div. Special Note: Gmail does not support embedded css. From there, Yahoo Beta will convert your embedded body styles to inline and place them inside the div it creates around your email content. To get around this, you can define your styles in the “body” type selector in your embedded CSS. Yahoo Beta strips your entire body tag along with each of its attributes. Yahoo! Mail strips your body tag by default. *Tools > Options > Content : Fonts & Colors > Advanced > Minimum Font Size (none)3. * "Allow pages to choose their own fonts, instead of my selections above"

*Tools > Options > Content : Fonts & Colors > Advanced *View > Zoom > Reset (Ctrl+0 (zero) Command+0 on Mac)

You can try different default fonts and temporarily disable website fonts to test the selected default font.
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You can do a font test to see if you can identify corrupted font(s).
