How to set username and password for SmtpClient object in .NET?

I see different versions of the constructor, one uses info from web.config, one specifies the host, and one the host and port. But how do I set the username and password to something different from the web.config? We have the issue where our internal smtp is blocked by some high security clients and we want to use their smtp server, is there a way to do this from the code instead of web.config?

In this case how would I use the web.config credentials if none is available from the database, for example?

public static void CreateTestMessage1(string server, int port)
{
    string to = "jane@contoso.com";
    string from = "ben@contoso.com";
    string subject = "Using the new SMTP client.";
    string body = @"Using this new feature, you can send an e-mail message from an application very easily.";
    MailMessage message = new MailMessage(from, to, subject, body);
    SmtpClient client = new SmtpClient(server, port);
    // Credentials are necessary if the server requires the client 
    // to authenticate before it will send e-mail on the client's behalf.
    client.Credentials = CredentialCache.DefaultNetworkCredentials;

    try {
        client.Send(message);
    }
    catch (Exception ex) {
        Console.WriteLine("Exception caught in CreateTestMessage1(): {0}", 
                    ex.ToString());
    }              
}

The SmtpClient can be used by code:

SmtpClient mailer = new SmtpClient();
mailer.Host = "mail.youroutgoingsmtpserver.com";
mailer.Credentials = new System.Net.NetworkCredential("yourusername", "yourpassword");

Use NetworkCredential

Yep, just add these two lines to your code.

System.Net.NetworkCredential credentials = new System.Net.NetworkCredential("username", "password");

client.Credentials = credentials;

M.Alaghemand

SmtpClient MyMail = new SmtpClient();
            MailMessage MyMsg = new MailMessage();
            MyMail.Host = "mail.eraygan.com";
            MyMsg.Priority = MailPriority.High;
            MyMsg.To.Add(new MailAddress(Mail));
            MyMsg.Subject = Subject;
            MyMsg.SubjectEncoding = Encoding.UTF8;
            MyMsg.IsBodyHtml = true;
            MyMsg.From = new MailAddress("username", "displayname");
            MyMsg.BodyEncoding = Encoding.UTF8;
            MyMsg.Body = Body;
            MyMail.UseDefaultCredentials = false;
            NetworkCredential MyCredentials = new NetworkCredential("username", "password");
            MyMail.Credentials = MyCredentials;
            MyMail.Send(MyMsg);

Since not all of my clients use authenticated SMTP accounts, I resorted to using the SMTP account only if app key values are supplied in web.config file.

Here is the VB code:

sSMTPUser = ConfigurationManager.AppSettings("SMTPUser")
sSMTPPassword = ConfigurationManager.AppSettings("SMTPPassword")

If sSMTPUser.Trim.Length > 0 AndAlso sSMTPPassword.Trim.Length > 0 Then
    NetClient.Credentials = New System.Net.NetworkCredential(sSMTPUser, sSMTPPassword)

    sUsingCredentialMesg = "(Using Authenticated Account) " 'used for logging purposes
End If

NetClient.Send(Message)

来源：https://stackoverflow.com/questions/2766928/how-to-set-username-and-password-for-smtpclient-object-in-net

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smtpclient