You may find that your emails fonts are much larger and tables appearing folded together. Luckily there is a way to fix this problem in Outlook!
HTML Email Knowledge Base
How you can have styles that only target the Yahoo! Mail Android app, using a simple workaround.
You can target the Yahoo! Mail iOS app by using the @media yahoo and adding a max-width to the media query.
You can target Outlook.com by using a CSS element called [owa] (Outlook Web Access), which is part of Outlook.com
You can target AOL Mail by using the CSS selector class .aolmail_ and adding your styles.