Which of the following is an email service provider?

An email service provider is a company that offers email services, allowing users to send and receive electronic messages. Gmail is a prime example of such a service, developed by Google, providing free email accounts.

• Gmail is correct as it is a widely used email service provider.
• "Windows 10" is incorrect because it is an operating system, not an email service.
• "Skype" is incorrect because it is primarily an instant messaging and video calling application, not an email service.
• "Facebook" is incorrect because it is a social media platform, not an email service provider.