The SMTP server requires a secure connection or the client was not authenticated

Question

I am getting this error

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTL         


        

Answer 1

This worked for me:

1. Need to turn on "Access for less secure apps" on google account(From Email).
2. Set smtpclient.UseDefaultCredentials = false;

3. Set smtpclient.EnableSsl = true;

       MailMessage mail = new MailMessage("FromEmail_Address", "ToEmail_Address");
       SmtpClient smtpclient = new SmtpClient();
       smtpclient.Port = 587;
       smtpclient.DeliveryMethod = SmtpDeliveryMethod.Network;
       smtpclient.UseDefaultCredentials = false;
       smtpclient.Host = "smtp.gmail.com";
       smtpclient.UseDefaultCredentials = false;
       mail.Subject = "Email Subject";
       mail.Body = "Content of the email";
       smtpclient.EnableSsl = true;
       smtpclient.Credentials = new System.Net.NetworkCredential()
       {
           UserName = "FromEmail_Address",
           Password = "password of the email"
       };
       client.Send(mail);
   

Answer 2

Actually you can handle this in your web.config file by adding enableSsl="true". This worked for me and I didn't need to do anything in code.

e.g.

<network host="smtp.gmail.com" enableSsl="true" ... />

Answer 3

Try setting the EnableSsl property to true:

smtpClient.EnableSsl = true;

AFAIK this property can only be set in code and cannot be specified in the config file.