无法使用 Gmail SMTP 发送电子邮件

Question

I have a web with contact form - I want feedback being sent to my gmail account. For this I created another, dummy gmail account for sending these messages. Code looks like this

                MailMessage msg = new MailMessage();
                msg.To.Add("to_mail@gmail.com");
                msg.From = new MailAddress("from_mail@gmail.com");                
                msg.Subject = "Feedback";
                msg.Body = txtName.Text + " " + txtEmail.Text + " " + txtMessage.Text;
                msg.IsBodyHtml = true;

                SmtpClient client = new SmtpClient();
                client.Host = "smtp.gmail.com"; 
                client.Port = 587;
                client.UseDefaultCredentials = false;
                client.Credentials = new System.Net.NetworkCredential("from_mail@gmail.com", "password");
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.EnableSsl = true;                    
                client.Send(msg);

This code works fine when I run it from localhost from my VS project, but once I compile it and upload to the web, its stops working with this error.

System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

Does anyone have an idea what caused it and how to fix it? I already enabled access for less secure applications in my gmail account. Tried also 465 port, but that doesnt work either.

Thank a lot, Jozef

Answer 1

Finally found an answer. Had to click this link with my "From" Gmail account logged in.

https://accounts.google.com/b/0/DisplayUnlockCaptcha

Answer 2

Possible Reason:

In gmail, If the current login region and the previous login region is different, then gmail ask us some security questions before login. So better try to login once via browser in the system which you are using that C# app.