会产生错误的代码如下
SmtpClient client = new SmtpClient("smtp服务器");
client.Credentials = new NetworkCredential("用户名", "密码");
client.UseDefaultCredentials = true;
MailMessage mess = new MailMessage();
mess.From = new MailAddress("发信人地址", "发信人姓名");
mess.To.Add(new MailAddress("收信人地址", "收信人姓名"));
mess.Subject = "主体";
mess.Body = "正文";
client.Send(mess);
MessageBox.Show("完成");
client.Credentials = new NetworkCredential("用户名", "密码");
client.UseDefaultCredentials = true;
MailMessage mess = new MailMessage();
mess.From = new MailAddress("发信人地址", "发信人姓名");
mess.To.Add(new MailAddress("收信人地址", "收信人姓名"));
mess.Subject = "主体";
mess.Body = "正文";
client.Send(mess);
MessageBox.Show("完成");
经过研究发现产生错误的原因是设置client.UseDefaultCredentials = true;属性放在了设置client.Credentials = new NetworkCredential("用户名", "密码");的后面,只要把这两行掉换一下位置就能正常发送邮件了.