当然，前提是得安装Jmail组件。

首先添加引用：

然后添加如下代码：
            jmail.Message jmessage = new jmail.MessageClass();
            jmessage.Charset = "GB2312";
            jmessage.From = textBox1.Text.ToString();
            jmessage.FromName = textBox1.Text.ToString();
            jmessage.ReplyTo = textBox1.Text.ToString();
            jmessage.Subject = textBox5.Text.ToString();
            jmessage.AddRecipient(textBox2.Text.ToString(), "Receive Name", "PGPKey");
            jmessage.Body = richTextBox1.Text.ToString();
            jmessage.MailServerUserName = textBox3.Text.ToString();
            jmessage.MailServerPassWord = textBox4.Text.ToString();
            try
            {
                jmessage.Send(comboBox1.Text.ToString(), false);
                MessageBox.Show("email sent successfully!");
                jmessage.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }