Visual studio 2010 SMTP电子邮件错误

我正在使用VisualStudio2010。当用户点击提交时，我正试图向1个电子邮件地址发送电子邮件。我得到的错误如下：

错误：语法错误，无法识别命令。服务器响应为：5.0.0在发送邮件之前，您的电子邮件系统必须进行身份验证：

以下是我的代码隐藏中的代码：

public void SendMail(string FromEmail, string ToEmail, string Subject, string Body)
    {
        System.Net.Mail.MailMessage eMail = new System.Net.Mail.MailMessage();
        eMail.From = new System.Net.Mail.MailAddress(FromEmail);
        //MailMessage eMail = new MailMessage();
        //eMail.From = new MailAddress(FromEmail);
        eMail.To.Add(ToEmail);
        eMail.Subject = Subject;
        eMail.IsBodyHtml = true;
        eMail.Body = Body;
        SmtpClient SMTP = new SmtpClient();
        //SMTP.Host = "mail.authsmtp.com";
        //SMTP.UseDefaultCredentials = true;
        //SMTP.EnableSsl = true;
        SMTP.Send(eMail);
        eMail.Dispose();
    } 




protected void btnSubmit_Click(object sender, EventArgs e)
        {

   StringBuilder sbBody = new StringBuilder();
                string FromEmail = "smit@college.edu";
                string ToEmail = "smit@college.edu";
                string Subject = "Application for" + " " + txtFirstName.Text + " " + txtLastName.Text + " " + "created on:" + " " + txtDateCreated.Text;
                sbBody.Append("Click link below to view application for" + " " + txtFirstName.Text + " " + txtLastName.Text);
                sbBody.Append("<br/>");
                sbBody.Append("<br/>");
                sbBody.Append("AdminDisplay.aspx?ID=@ID");
                sbBody.Append("<br/>");
                sbBody.Append("Thank you,");
                sbBody.Append("Admin");
                SendMail(FromEmail, ToEmail, Subject, sbBody.ToString());  

            }

这是我的web.config：

<system.net>
        <mailSettings>
            <smtp from="smit@college.edu">
                <network host="mail.authsmtp.com" defaultCredentials="true" />
            </smtp>
        </mailSettings>
    </system.net>

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我一天大部分时间都在做这个，需要让它工作起来。谢谢

您使用Exchange吗？我知道我们的Exchange管理员必须启用PC和服务器以发送电子邮件。很抱歉，我不能说得更具体-我对Exchange一无所知。您的SMTP服务器可能还需要凭据。和设置它的人核实一下。