Both IMAP and POP3 are the client-server email retrieval protocols. While POP3 can be considered a "store-and-forward" service because email is saved for particular users in a single mailbox on the server and is moved from the server to the local device when the mail client opens. In contrast, IMAP is a remote file server because the user can store the email on the server and read or access it from any device or location as needed.