Cannot send secure mail thru System.Net.Mail.SmtpClient using Outlook365 Mail Server since February - Progress Community
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C# : System.Net.Mail.SmtpException: The operation has timed out. error in asp.net send mail code usi - YouTube
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c# - The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required? - Stack Overflow
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c# - SmtpException: Unable to read data from the transport connection: net_io_connectionclosed - Stack Overflow
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SystemNetMailSmtpException The SMTP server requires a secure connection or the client was not authenticated
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c# - SSIS script task failing to send email SMTPexception:System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed - Stack Overflow
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Incoming E-Mails with Attachments Failed - "Message size exceeds fixed maximum message size" - SharePoint Diary
![c# - System.Net.Mail.SmtpException: 'The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Auth - Stack Overflow c# - System.Net.Mail.SmtpException: 'The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Auth - Stack Overflow](https://i.stack.imgur.com/dNi26.png)