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9 TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
9 TCP/IP Key Applications and Application Protocols
9 TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
9 TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
9 TCP/IP Electronic Mail Access and Retrieval Protocols and Methods
9 TCP/IP Internet Message Access Protocol (IMAP/IMAP4)
IMAP Not Authenticated State: User Authentication Process and Commands
(Page 2 of 2)
IMAP Authentication Methods
The authentication methods are:
- Plain Login: This is the typical
username / password technique, using the LOGIN command
by itself. This is similar to the
simple scheme used in POP3, except that
in IMAP4 one command is used to send both the user name and password.
Since the command and parameters are sent in plain text, this is by
far the least secure method of authentication and is not recommended
by the standard unless some other means is used in conjunction.
- TLS Login: This is a secure
login where the Transport Layer Security (TLS) protocol is first enabled
with the STARTTLS command, and then the LOGIN command
can be used securely. Note that STARTTLS only causes the TLS
negotiation to begin, and does not itself cause the IMAP client to be
authenticated. Either LOGIN or AUTHENTICATE must still
- Negotiated Authentication Method:
The AUTHENTICATE command allows the client and server to use
any authentication scheme that they both support. The server may indicate
which schemes it supports in response to a CAPABILITY command.
After specifying the authentication mechanism to be used, the server
and client exchange authentication information as required by the mechanism
specified. This may require one or more additional lines of data to
In response to a LOGIN or
AUTHENTICATE command, the server will send an OK
message if the authentication was successful, and then transition to
the Authenticated state. It will send a NO response
if authentication failed due to incorrect information. The client can
then try another method of authenticating, or terminate the session
with the LOGOUT command.
Key Concept: IMAP supports three basic types of authentication: a plain username/password login; authentication using Transport Layer Security; or the negotiation of some other authentication method between the client and server. In some cases, the IMAP server may choose to preauthenticate clients that it is able to reliably identify, in which case the Not Authenticated state is skipped entirely.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
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