In this method, you’ll create a new label and filter for notes that only work for new emails. With this method, you will not be able to take notes on existing emails or send notes in reply to an email.
When you click Create filter, you’ll see another pop-up window.
Click Create filter to continue.
Use notes sent in Gmail to remind yourself about daily, weekly or monthly events in your calendar. You can send notes to yourself using any email address (not just your Gmail address).
Many of these Gmail extensions offer you features so you can highlight or take notes on existing emails. You can also use Google Keep, which is another Google service that offers note-taking productivity.