C＃SMTP虚拟服务器不发送邮件

Question

C# SMTP virtual server doesn't send mail. Here's the code:

public static void SendEmail(string _FromEmail, string _ToEmail, string _Subject, string _EmailBody)
{

    // setup email header . 
    SmtpMail.SmtpServer = "127.0.0.1";
    MailMessage _MailMessage = new MailMessage();

    _MailMessage.From = _FromEmail;
    _MailMessage.To = _ToEmail;
    _MailMessage.Subject = _Subject;
    _MailMessage.Body = _EmailBody;

    try
    {
        SmtpMail.Send(_MailMessage);
    }
    catch (Exception ex)
    {
        if (ex.InnerException != null)
        {
            String str = ex.InnerException.ToString();

        }
    }

Answer 1

It is an Interop exception because that .NET code is relying on Interop(erability) services, non-managed stuff. The message however is pretty clear, the server is unable to relay because it has been configured to reject relaying of emails.

Many years ago that was not a problem and you could virtually use any public SMTP server to send emails. With the advent of SPAM the whole game changed, now in most servers relaying is disabled and your mail send request is rejected.

What you will need here so that it does not reject your mail, is to authenticate your request (account/user and password on that server). It has to be a valid username & password combination known to that SMTP server. You do that by setting those (out of my head sorry) in the .Credentials property. See also the UseDefaultCredentials property, if you set Credentials you need to make sure UseDefaultCredentials is false.

Answer 2

If the error is this:

550 5.7.1 Unable to relay for ragaei.mahmoud@invensys.com

Then your SMTP server cannot send to that email address. Use a different SMTP server or configure it to relay out to the internet. The local one will probably only send to addresses on your own domain. If this is an SMTP server configuration question, you may have more luck asking on Superuser.