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 = "[email protected]";
string from = "[email protected]";
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");

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)

Use `NetworkCredential`

Yep, just add these two lines to your code.

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

client.Credentials = credentials;

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);

There are a couple of things not mentioned in other answers.

First, it can be necessary to use `CredentialCache` instead of `NetworkCredential` directly, in order to specify different authentication schemes.

In the documentation, the SMTP authentication type names are listed as:

> "NTLM", "Digest", "Kerberos", and "Negotiate"

However I had to breakpoint within the .NET code to see that the value being passed for "AUTH LOGIN" was actually "login". This seems to happen automatically anyway, so this is only necessary to use different schemes.

Second, though no one here is, you probably do NOT want to specify a domain name in your `NetworkCredential`. Doing so results in `SmtpClient` passing a username of the form `example.com\username` which is almost guaranteed to not be accepted by a mail server. (And if your mail server is loose with its authentication requirements, you may not know that you are failing to authenticate.)

```
var nc = new NetworkCredential(
username,
password
// no domain!
);

// only if you need to specify a particular authentication scheme,
// though it doesn't hurt to do this anyway if you use the right scheme name
var cache = new CredentialCache();
cache.Add(smtpServerName, port, "NTLM", nc);
// can add more credentials for different combinations of server, port, and scheme

smtpClient.Credentials = cache;
```

Lastly, note that you do not need to set `UseDefaultCredentials` if you are also setting `Credentials` as they are both based on the same underlying value. Setting both can lead to issues since they will just overwrite each other.

If in doubt, use WireShark and disable SSL temporarily (to see the network frames or else they are encrypted), and confirm that your SMTP authentication is working. (Use an "smtp" filter in WireShark).