Using TLS 1.2 with SMTP

By default most systems allow SSL 3.0, TLS 1.0, 1.2 and 1.2 to be used, when connecting using SMTP client.

TLS 1.2 is the most secure version of SSL/TLS protocols. It is easy to force the connection to use it. All you need to do is to set Smtp.SSLConfiguration.EnabledSslProtocols property to SslProtocols.Tls12:

// C#

using (Smtp smtp = new Smtp())
{
    smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    smtp.ConnectSSL("smtp.example.com");

    smtp.UseBestLogin("user","password");

    // ... 

    smtp.Close();
}

' VB.NET

Using smtp As New Smtp()
	smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	smtp.ConnectSSL("smtp.example.com")

	smtp.UseBestLogin("user@example.com", "password")

	'...

	smtp.Close()
End Using

For explicit SSL/TLS, code is almost the same. You first connect to non-secure port and secure the connection using Smtp.StartTLS command:

// C#

using (Smtp smtp= new Smtp())
{
    smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12;

    smtp.Connect("smtp.example.com");
    smtp.StartTLS();

    smtp.UseBestLogin("user@example.com","password");

    // ... 
    
    smtp.Close();
}

' VB.NET

Using smtp As New Smtp()
	smtp.SSLConfiguration.EnabledSslProtocols = SslProtocols.Tls12

	smtp.Connect("smtp.example.com")
	smtp.StartTLS()

	smtp.UseBestLogin("user@example.com", "password")

	'...

	smtp.Close()
End Using

To use TLS 1.2 at least .NET Framework 4.5+ must be installed on your machine and you application should target .NET 4.5+.

It is possible to use TLS 1.2 in applications targeting earlier .NET framework versions, but 4.5 must be installed on the machine. After you have .NET 4.5 installed, your 2.0-4.0 apps will use the 4.5 System.dll and you can enable TLS 1.2 using this code:

// C#

imap.SSLConfiguration.EnabledSslProtocols = (SecurityProtocolType)3072;