APOP authentication does not require your account password to be sent as plain text to the POP3 mail server, however, not all Internet providers support it.

POP3 Post Office Protocol (POP3 RFC 1939) Version 3 is a standard internet protocol used for retrieving Internet email. It is used by your email client (Eudora, Netscape Communicator, MS Outlook, etc.) to communicate with a SMTP mail server.

Difference between "POP" and "IMAP"

Post Office Protocol (POP), emails are delivered to a mail server, users connects to the mail server and download mails and save them in their mail client (email program).

IMAP4
Internet Message Access Protocol Version 4
are used, to hold email messages and allows users to view message heading www.imc.org/rfc2060 or www.imap.org

IMAP4
allows a client (email program) to access and manipulate email messages on a remote mail server as if they were local, without the need to download the message or to deliver the message to mail readers and can relay the email message to SMTP mail servers using POP3

IMAP4
does not specify a means of posting mail--this function is handled by a mail transfer protocol such as SMTP

Mail readers - or mail user agents
allows you to read emails residing in your mailbox on the mail server or download it onto your desktop pcs mail client.

User Agents
 A program (ie: Eudora) or editor that let users create, edit, compose, store and send mails to a mail server, polls a mail server for mails, download and display mails, as well as using POP3 to talk to mail servers.