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When the SMTP server requires a secure connection, it means that the connection between the client and the server needs to be encrypted, usually through SSL or TLS. This is to ensure that any sensitive information, such as login credentials or message contents, is not intercepted or tampered with during transit.

If the client is not authenticated, it means that the SMTP server is not recognizing or accepting the credentials provided by the client to establish the connection. This could be due to incorrect login details, lack of authorization, or other authentication issues. The client will need to provide valid credentials to successfully connect to the SMTP server and send messages.