ClientCertificates Property

SmtpClient.ClientCertificates Property


Specify which certificates should be used to establish the Secure Sockets Layer (SSL) connection.

Namespace:   System.Net.Mail
Assembly:  System (in System.dll)

public X509CertificateCollection ClientCertificates { get; }

Property Value

Type: System.Security.Cryptography.X509Certificates.X509CertificateCollection

An X509CertificateCollection, holding one or more client certificates. The default value is derived from the mail configuration attributes in a configuration file.

Client certificates are, by default, optional; however, the server configuration might require that the client present a valid certificate as part of the initial connection negotiation.


The Framework caches SSL sessions as they are created and attempts to reuse a cached session for a new request, if possible. When attempting to reuse an SSL session, the Framework uses the first element of ClientCertificates (if there is one), or tries to reuse an anonymous sessions if ClientCertificates is empty.


The Framework attempts to reuse an SSL session only if a client certificate is not required.

The following code example establishes an SSL connection with the SMTP server and uses the connection to send an email.

public static void CreateTestMessage(string server)
	string to = "";
	string from = "";
	MailMessage message = new MailMessage(from, to);
	message.Subject = "Using the new SMTP client.";
	message.Body = @"Using this new feature, you can send an e-mail message from an application very easily.";
	SmtpClient client = new SmtpClient(server);
	// Credentials are necessary if the server requires the client 
	// to authenticate before it will send e-mail on the client's behalf.
	client.UseDefaultCredentials = true;
                      client.EnableSsl = true;

.NET Framework
Available since 2.0
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