使用.net中的SmtpClient发送邮件

Question

I am unable to send the mail using smtp client. here is the code:

SmtpClient client=new SmtpClient("Host");
client.Credentials=new NetworkCredential("username", "password");
MailMessage mailMessage = new MailMessage();
mailMessage.from="sender@gmail.com";
mailMessage.To.Add("recipient@gmail.com");
mailMessage.body="body";
mailMessage.subject="subject";
client.Send(mailMessage);

The problem is that when I use this code in ASP.NET application, I do not receive any mails. When in asp.net I change the from mail address to username given in NetworkCredential, I receive mails.

But in C# windows application, I can get emails, even if sender's email address is not valid.

Answer 1

I figured out that setting the SmtpClient Credentials property before setting the ' UseDefaultCredentials = false ' UseDefaultCredentials = false causes the credentials to be ignored.

Fails:

SmtpClient smtp = new SmtpClient;
smtp.Credentials = new NetworkCredential("user","pass");
smtp.UseDefaultCredentials = false;

Works:

SmtpClient smtp = new SmtpClient;
smtp.UseDefaultCredentials = false;
smtp.Credentials = new NetworkCredential("user","pass");

Go figure.

Answer 2

It means your mail server does not allow Mail-Relay. Your mail server only allows you to send mail from authenticated email-id as username. Generally this is done to prevent mails being sent as different identities other than the authenticated one.

Answer 3

Try this :

MailMessage mail = new MailMessage("emailfrom","emailto");

mail.From = new MailAddress("emailfrom");
mail.Subject = txtsbjct.Text;
string Body = txtmsg.Text;
mail.Body = Body;

mail.IsBodyHtml = true;
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.gmail.com"; //Or Your SMTP Server Address
smtp.Credentials = new System.Net.NetworkCredential("youremail", "yourpassword");

smtp.EnableSsl = true;
smtp.Send(mail);
txtemail.Text = "";
txtmsg.Text = "";
txtsbjct.Text = "";
Label1.Text = "your email has been send";
mail = null;
smtp = null;

Answer 4

The short answer : Do not use .net the internal SMTP client class - use MailKit .

The long answer :

1. It is marked as obsolete in MS docs

[System.Obsolete("SmtpClient and its network of types are poorly designed, we strongly recommend you use https://github.com/jstedfast/MailKit and https://github.com/jstedfast/MimeKit instead")] public class SmtpClient : IDisposable

1. Use the oss lib MailKit .
2. Elaboration : Because you will face its deficiencies sooner rather than later. Read here or read around the internet.
3. Here is an example for sending plain messages and multipart messages.

I intentionally did not copy-paste the examples from the docs here because the documentation may change over time and it is better to read .

Answer 5

void sendEmail(string strFrom
                        , string strTo
                        , string strSubject
                        , string strBody)
   {

       MailMessage objMailMessage = new MailMessage();
       System.Net.NetworkCredential objSMTPUserInfo =
           new System.Net.NetworkCredential();
       SmtpClient objSmtpClient = new SmtpClient();

       try
       {
           objMailMessage.From = new MailAddress(strFrom);
           objMailMessage.To.Add(new MailAddress(strTo));
           objMailMessage.Subject = strSubject;
           objMailMessage.Body = strBody;

           objSmtpClient = new SmtpClient("172.0.0.1"); /// Server IP
           objSMTPUserInfo = new System.Net.NetworkCredential
           ("User name", "Password","Domain");
           objSmtpClient.Credentials = objSMTPUserInfo;
           objSmtpClient.UseDefaultCredentials = false;
           objSmtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;

           objSmtpClient.Send(objMailMessage);
       }
       catch (Exception ex)
       { throw ex; }

       finally
       {
           objMailMessage = null;
           objSMTPUserInfo = null;
           objSmtpClient = null;
       }
   }