What’s new in Mail?
The Mail app in macOS High Sierra offers new features for sending, receiving, and viewing email.
When you use Mail full screen, messages open in Split View, side-by-side with the message list. You can easily read and write messages without having to switch windows. For more information, see Use Mail full screen.
When you search for messages in Mail, Top Hits shows the most relevant messages at the top of the search results. Top Hits reflects the messages you’ve read and replied to recently, your VIP senders and contacts, and other factors. For more information, see Search for messages.
When you write a message, you can choose a background color for text from the Format toolbar. For more information, see Format text in messages.