The TCP/IP Guide  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 General Operation, Client/Server Communication and Session States 1 2 3 4 IMAP Not Authenticated State: User Authentication Process and Commands

Command Groups

IMAP commands are organized into groups based on which session states the IMAP session may be in when they are used. These groups are:

• “Any State” Commands: A small number of commands that can be used at any time during an IMAP session.
  
  
• Not Authenticated State Commands: Commands that can be used only in the Not Authenticated state. They are usually used for authentication, of course.
  
  
• Authenticated State Commands: These commands are used to perform various actions on mailboxes. (Note that despite the name, these commands can also be used in the Selected state.)
  
  
• Selected State: A set of commands for accessing and manipulating individual messages that can be used only in the Selected state.

The reason for having the distinct Authenticated and Selected states and command groups is that IMAP is designed specifically to enable the manipulation of multiple mailboxes. After the session starts and the client is authenticated, the client is allowed to issue commands that work with entire mailboxes. However, it may not issue commands that manipulate individual messages until it tells the server which mailbox it wants to work with, which puts it in the Selected state. The client can also issue mailbox commands from the Selected state.

IMAP General Operation, Client/Server Communication and Session States 1 2 3 4 IMAP Not Authenticated State: User Authentication Process and Commands