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https://blog.devoworx.net/2012/05/09/the-smtp-server-requires-a-secure-connection-or-the-client-was-not-authenticated-the-server-response-was-5-7-1-client-was-not-authenticated/
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.1 Client was not authenticated