Post Office Protocol 3 provides a simple, standard way for individuals to access remote mail servers and download messages to a mailbox on their computer. POP3 mail servers are hosted by Internet Service Providers (Cox Cable,  Road-Runner, AT&T, etc.)

Storage Location

Email is delivered to the ISP mail server. When the individual logs in and accesses their email account using an email client, new emails are downloaded to the individual’s computer, then removed from the mail server.* 
* email can remain on the server, however, it is usually limited by time (<30 days) or space (<100MB) and requires the individual to configure the option.