Following on, here is the error manager give:
System.IO.IOException: System.IO.IOException: The authentication or decryption has failed. ---> System.IO.IOException: The authentication or decryption has failed. ---> Mono.Security.Protocol.Tls.TlsException: The authentication or decryption has failed.
at Mono.Security.Protocol.Tls.RecordProtocol.EndReceiveRecord (System.IAsyncResult asyncResult) [0x00040] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
at Mono.Security.Protocol.Tls.SslClientStream.SafeEndReceiveRecord (System.IAsyncResult ar, System.Boolean ignoreEmpty) [0x00000] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
at Mono.Security.Protocol.Tls.SslClientStream.NegotiateAsyncWorker (System.IAsyncResult result) [0x00071] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
--- End of inner exception stack trace ---
at Mono.Security.Protocol.Tls.SslClientStream.EndNegotiateHandshake (System.IAsyncResult result) [0x0003b] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (System.IAsyncResult asyncResult) [0x0000c] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
--- End of inner exception stack trace ---
at Mono.Security.Protocol.Tls.SslStreamBase.EndRead (System.IAsyncResult asyncResult) [0x00057] in <1d0bb82c94e7435eb09324cf5ef20e36>:0
at Mono.Net.Security.Private.LegacySslStream.EndAuthenticateAsClient (System.IAsyncResult asyncResult) [0x00011] in :0
at Mono.Net.Security.Private.LegacySslStream.AuthenticateAsClient (System.String targetHost, System.Security.Cryptography.X509Certificates.X509CertificateCollection clientCertificates, System.Security.Authentication.SslProtocols enabledSslProtocols, System.Boolean checkCertificateRevocation) [0x0000e] in :0
at System.Net.Mail.SmtpClient.InitiateSecureConnection () [0x0005e] in :0
at System.Net.Mail.SmtpClient.SendCore (System.Net.Mail.MailMessage message) [0x000b9] in :0
at System.Net.Mail.SmtpClient.SendInternal (System.Net.Mail.MailMessage message) [0x00050] in :0
at System.Net.Mail.SmtpClient.Send (System.Net.Mail.MailMessage message) [0x0009c] in :0