Emoji were already almost everywhere. Everywhere, that is, except in Gmail. Would you even want your email service to provide this functionality? Well, whether you do or you don't, it's now here. Gmail is getting emoji reactions, starting on Android phones and tablets. Undoubtedly, if this proves popular, it will quickly spread to iOS and the web. Similarly to how your favorite chat app already does it, emoji reactions will be available on each Gmail message. Once you've opened a message, scroll down and you'll find the new emoji reaction button to the right of Reply, Reply all, and...
Source: https://www.gsmarena.com/gmail_now_has_emoji_reactions_for_better_or_worse-news-60100.php