Email Service Provider
Email service provider (ESP) refers to an organization or software platform that allows you to host and manage your email accounts within their infrastructure.
Often confused with the email marketing or email automation platforms, ESPs serve a different purpose and usually aren’t as feature-rich. Also known as mailbox providers, some of the most popular examples are Gmail and Outlook.
An email client is a mobile or desktop application that offers a convenient interface to manage your email account, i.e., send and receive messages. It usually connects directly to your ESP.