Login is a virtual procedure in TIdIMAP4 used to perform authentication for the IMAP4 account. Login allows the IMAP4 session to switching users that are on the same server without having to disconnect from the server. 

For connections that support TLS (Transport Layer Security) and contain an explicit TLS value in UseTLS, the STARTTLS command is used to perform TLS handshaking and negotiation. 

For non-TLS transports, the value in the AuthType property indicates if the Username and Password properties are used for authentication, or if the SASLMechaisms and Capabilities propeties are used for authentication. 

Login updates the value in ConnectionState to reflect the current status of the authentication process. 

If an exception occurs in the Login method, the connection is closed by calling the Disconnect method prior to exit. 

Login is called in the Connect method when arguments to the method indicate automatic logins should be performed.

Connect ConnectionState UseTLS AuthType Disconnect SASLMechanisms Capabilities