2.2.12 [RFC3501] Section 6.2, Client Commands — Not Authenticated State
The specification states that server implementations MAY allow access to certain mailboxes without establishing authentication.
Microsoft Exchange Server 2007, Microsoft Exchange Server 2010, Microsoft Exchange Server 2013, Microsoft Exchange Server 2016
Microsoft Exchange Server does not allow access to mailboxes without authentication.
The specification states that a client can access mailboxes without establishing authentication by using either the ANONYMOUS authenticator or the LOGIN command with a user name of "anonymous".
Exchange 2007, Exchange 2010, Exchange 2013, Exchange 2016
Microsoft Exchange does not support either the ANONYMOUS authenticator or the LOGIN command with an anonymous user name.