One of the features that many email applications, such as Gmail, include is an importance indicator. In Gmail, emails are marked as important when Google thinks that they are likely to be something you want to read. Google determines this through an analysis process based on your interactions with the emails you receive. Factors include: who you email and how often you email them, which emails you open, which emails you reply to, keywords that are in emails that you usually read, and which emails you star, archive or delete.
Tip: Gmail shows why emails were marked as important if you hover your mouse over the yellow important marker, but this generally just says “The email was sent directly to you” or “Through Google magic” rather than providing a more concrete reason.
You can choose to teach Google which emails you think are important by manually marking each email you receive as important or not. Google will use this data to tailor its algorithm for you. If you don’t want Google to monitor your actions with regards to emails, you can disable it in the settings, alternatively, you can disable the “Important” markers altogether.
To be able to access the settings, click on the cogwheel icon in the top-right corner, then click “See all settings”.
You can find the importance marker options second from the bottom of the “Inbox” tab in Gmail’s settings. In the “Importance marker” section there are two pairs of radio buttons. The top pair allows you to enable or disable importance markers outright, while the bottom pair allows you to prevent Google from analysing your usage to predict which emails you will think are important.