Post Office Protocol (POP) Question:

An email client, email reader, or more formally mail user agent (MUA), is a computer program used to manage email.

Specifically, the term email client may refer to any agent acting as a client toward an email server, regardless of it being a mail user agent, a relaying server, or a human typing on a terminal. In addition, a web application providing message management, composition, and reception functionality is sometimes considered an email client.