The IMAP4 Extensions are composed of three distinct extensions:
The Internet Message Access Protocol - Version 4 (IMAP4) NTLM extension
The IMAP4 delegate access extension
The IMAP UIDPLUS extension
The IMAP4 NTLM extension enables a client to authenticate to a server using NTLM authentication. It allows the client to send an NTLM message over a standard IMAP4 connection and the server to send a response indicating the success or failure of the authentication.
The IMAP4 delegate access extension enables a client to access a mailbox on the server as a user other than the mailbox owner. This enables client access in the scenario where the mailbox owner has granted delegate access to their mailbox.
The IMAP UIDPLUS extension described in [RFC4315] enables a client to selectively remove messages from the server.