Gmail provides a variety of tools to help ensure your emails are well formatted and actionable.
CSS in email
Gmail supports a rich subset of CSS properties & media queries to help you ensure that your message is formatted the way you intended, whether it's viewed on a phone in portrait mode, a desktop screen, or a landscaped tablet. As an email designer, you can now change styles based on width, rotation, and resolution to allow responsive formatting tailored to the recipient's device.
<style> tags can now be included in HTML bodies,
eliminating the need to use inline styles.
Emails can include additional semantic markup that affects how messages are displayed. Markup helps make information available across a user's Google experience, and makes it easy for users to take quick action on important items.
The bulk sender guidelines provide useful tips for ensuring your content is received. Some senders may also be eligible to use Gmail Postmaster Tools which provide senders with metrics on parameters such as reputation and spam rate. It can help you check compliance to the Gmail bulk sender guidelines, as well as identify issues that can cause trouble with the spam filter.