我正在尝试使用C＃发送电子邮件（SMTP），但是有一个例外，“发送电子邮件失败”。

我在代码中启用了SSL，并使用465端口（已打开）通过system.net.mail库将电子邮件发送到Yahoo（smtp.mail.yahoo.com）。

try
{
    string mass = " Hi,this is a compo team email to you for a verification code! Your verification code is: ''" + result + "'' You can enter this code to your compex for go ahead!!!";

    string frommail = "<my mail is here>";
    string tomail = emailtxt.Text;
    string submail = "verification";
    string smtptext = "smtp.mail.yahoo.com";
    string passmail = "<my email password here> ";
    MailMessage mail = new MailMessage(frommail,tomail,submail,mass);
    SmtpClient client = new SmtpClient(smtptext);
    client.Port = 465;
    client.Credentials = new System.Net.NetworkCredential(frommail,passmail);
    client.EnableSsl = true;
    client.Send(mail);
    MessageBox.Show("email sent","log",MessageBoxButtons.OK);
    /////email
}
catch (Exception exc)
{
    MessageBox.Show(exc.Message);
}

我该如何解决？怎么了？