Give me a list of free email service provider other than Gmail.

1. Outlook: It is offering from Microsoft, and is considered a powerful email service. It integrates with other Microsoft service ecosystem and used by large business enterprises.
2. Proton: Formerly called ProtonMail, has a unique offering when it comes to privacy protecting email service provided and hence has a very unique service offering.
3. Yahoo! Mail: Yahoo offers this very mature email service and has a lot of custom inbox and themes options.
4. Zoho Mail: Another email provider that provided fully encrypted data and privacy protection. On the top, it also provides a very easy to use email migration service.