I use Protonmail as they offer quite a bit of privacy, offer lots of features, and are free. I particularly like that they protect from tracking pixels notifying the company you read the email.
Proton Mail: Get a free email account with privacy and encryption | Proton
Proton Mail is the world’s largest secure email service with over 100 million users. Available on Web, iOS, Android, and desktop. Protected by Swiss privacy law.