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By default, POP3
clients login to the POP3 server by sending the password (as text)
for the mail account. This may be undesirable in high security-type
situations.
With POP3's optional APOP authentication, the password itself is
never sent to the remote mail server. Instead, a digest is created using the RSA MD5 algorithm.
This digest is based
on the password and a unique value supplied by the POP3 mail server
during the connection.
This digest is sent to the mail server in lieu of the
password. Because the unique value supplied by the mail server changes with
each connection.
A POP authentication ensures that a different digest will be
sent each time you log onto the sever and reduces the ability for a network
sniffing program to capture password.
APOP is a POP3
setting that encrypts your username and password, an authentication mechanism designed to protect your POP3 account
password when checking mail.
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.
A POP3 session
is created when a remote user connects to a mailbox on the POP3 mail
server. The session ends when the remote user disconnects from the POP3 mail
server.
While a session is open, no other user can retrieve mail from the POP3
mailbox, however mail can still be sent to that account. This is by design of
the POP3 protocol.
While in a session,
regardless of new mail which may be arriving in the mailbox, all things remain
equal. At the time the session is initiated, mailbox state is saved and the
entire session operates off of that cached state.
Once a session is
terminated, values obtained
from that session may no longer be valid.
Therefore,
if you initiate a session with a POP3 mail server and find that there are five
messages available. While in the session, operations on these messages require
a message number, which is the position of the message in the list of five.
Once you terminate
your session, you can not assume that five messages are still
available. If you initiate another session, you can not assume that the
message number three from the first session is message number three in the new
session.
Because of this,
certain message operations are only valid while in the same session which
downloaded the message.
Once a session is terminated, if you wish to perform
server operations on a specific message, you will need to establish a new
session, locate the message by comparing its properties (subject, date,
message id, etc...) to ones you saved from the previous session, and then act
upon the message before terminating the new session.
See
Post Office Protocol (POP3
RFC 1939)
Version 3 - The Standard internet protocol used for retrieving Internet email.
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Other protocols involved in sending and receiving
of e-mails.
MTA - Message Transfer
Agent the exchange of mail using TCP/IP
is performed by MTA that defines how email messages are transmitted between
two users.
Email Daemon
- An email software program residing in a mail server that manages incoming and
outgoing mails.
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