2.2.7 Standards Support Protocol Extensions

Exchange servers support a number of different standard protocols for e-mail (POP3, SMTP, IMAP4, and WebDAV) and directory information (LDAP). The protocol extensions in this table describe extensions to these standards primarily for authentication and authorization.

Protocol extension name


Short name

Internet Message Access Protocol Version 4 (IMAP4) Extensions

Provides an authentication mechanism based on the NT LAN Manager (NTLM) Authentication Protocol, a delegate access mechanism to allow a delegate to access a delegator's mailbox, and support for the IMAP UIDPLUS extension described in [RFC4315].


Lightweight Directory Access Protocol (LDAP) Version 3 Extensions

Extends LDAPv3, which enables directory access.


Post Office Protocol Version 3 (POP3) Extensions

Extends POP3, as described in [RFC1939], which enables the listing and downloading of mail.


Simple Mail Transfer Protocol (SMTP) Extensions

Extends SMTP standards to facilitate authentication and negotiation between a client and a server and to enable the server to close connections that exceed configured thresholds.


SMTP Protocol: AUTH LOGIN Extension

Extends SMTP to support a simple base64 encoding authentication mechanism.


OAUTH 2.0 Authorization Protocol Extensions

Extends the OAuth 2.0 Authentication Protocol: SharePoint Extensions and the JSON Web Token (JWT) to enable server-to-server authentication.