gmail smtp mail the SMTP server requires a secure connection or the client was not authenticated Edit
gmail smtp mail the SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at
check this article C# send email using gmail smtp to send mail from gmail
while trying to send an email from your C# code using gmail SMTP you might get this error. This might be because the user was not authenticated. Or this can also be because Gmail is blocking the mail from your application. If Gmail is blocking your mail, open the mail from Gmail and see if you have received a mail from Gmail.
Critical security alertSign-in attempt was blocked Someone just used your password to try to sign in to your account from a non-Google app. Google blocked them, but you should check what happened. Review your account activity to make sure no one else has access.
The solution is to enable less secure apps in your Gmail account.
1. Open gmail 2. Top Right menu select "Manage Your Google Account"
3. Select Security from the left menu
4. Scroll down and enable less secure apps
Once this has been enabled you will be able to send smtp mail from gmail using less secure apps.