从网络主机发送电子邮件，无需使用用户名和密码

我已经编写了一个C#程序来发送电子邮件，它非常有效。此外，我有一个发送电子邮件的PHP脚本，它也非常好用。

但我的问题是：是否可以像在PHP中那样使用C#发送电子邮件，在那里您不需要指定凭据、服务器、端口等。

我想用C#代替PHP，因为我正在创建一个ASP.Net web应用程序。

这是我当前的C#代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net.Mail;
using System.Net;
namespace $rootnamespace$
{
public partial class $safeitemname$ : Form
{
    public $safeitemname$()
    {
        InitializeComponent();
    }
    private void AttachB_Click(object sender, EventArgs e)
    {
        if (AttachDia.ShowDialog() == DialogResult.OK)
        {
            string AttachF1 = AttachDia.FileName.ToString();
            AttachTB.Text = AttachF1;
            AttachPB.Visible = true;
            AttachIIB.Visible = true;
            AttachB.Visible = false;
        }
    }
    private void AttachIIB_Click(object sender, EventArgs e)
    {
        if (AttachDia.ShowDialog() == DialogResult.OK)
        {
            string AttachF1 = AttachDia.FileName.ToString();
            AttachIITB.Text = AttachF1;
            AttachPB.Visible = true;
        }
    }


    private void SendB_Click(object sender, EventArgs e)
    {
        try
        {
            SmtpClient client = new SmtpClient(EmailSmtpAdresTB.Text);
            client.EnableSsl = true;
            client.Timeout = 20000;
            client.DeliveryMethod = SmtpDeliveryMethod.Network;
            client.UseDefaultCredentials = false;
            client.Credentials = new NetworkCredential(EmailUserNameTB.Text, EmailUserPasswordTB.Text);
            MailMessage Msg = new MailMessage();
            Msg.To.Add(SendToTB.Text);
            Msg.From = new MailAddress(SendFromTB.Text);
            Msg.Subject = SubjectTB.Text;
            Msg.Body = EmailTB.Text;
            /// Add Attachments to mail or Not
            if (AttachTB.Text == "")
            {
                if (EmailSmtpPortTB.Text != null)
                    client.Port = System.Convert.ToInt32(EmailSmtpPortTB.Text);
                client.Send(Msg);
                MessageBox.Show("Successfuly Send Message !");
            }
            else 
            {
                Msg.Attachments.Add(new Attachment(AttachTB.Text));
                Msg.Attachments.Add(new Attachment(AttachIITB.Text));
                if (EmailSmtpPortTB.Text != null)
                client.Port = System.Convert.ToInt32(EmailSmtpPortTB.Text);
                client.Send(Msg);
                MessageBox.Show("Successfuly Send Message !");
            }

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }
    private void settingsBindingNavigatorSaveItem_Click(object sender, EventArgs e)
    {
        this.Validate();
        this.settingsBindingSource.EndEdit();
        this.tableAdapterManager.UpdateAll(this.awDushiHomesDBDataSet);
    }
    private void awDushiHomesEmail_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'awDushiHomesDBDataSet.Settings' table. You can move, or remove it, as needed.
        this.settingsTableAdapter.Fill(this.awDushiHomesDBDataSet.Settings);
    }
  }
}

这是在PHP中完成的方式：

<?php
//define the receiver of the email
$to = 'test@hotmail.com';
//define the subject of the email
$subject = 'Test email with attachment';
//create a boundary string. It must be unique
//so we use the MD5 algorithm to generate a random hash
$random_hash = md5(date('r', time()));
//define the headers we want passed. Note that they are separated with 'r'n
$headers = "From: webmaster@example.com'r'nReply-To: webmaster@example.com";
//add boundary string and mime type specification
$headers .= "'r'nContent-Type: multipart/mixed; boundary='"PHP-mixed-".$random_hash."'"";
//read the atachment file contents into a string,
//encode it with MIME base64,
//and split it into smaller chunks
$attachment = chunk_split(base64_encode(file_get_contents('PDFs'Doc1.pdf')));
//define the body of the message.
ob_start(); //Turn on output buffering
?>
--PHP-mixed-<?php echo $random_hash; ?> 
Content-Type: multipart/alternative; boundary="PHP-alt-<?php echo $random_hash; ?>"
--PHP-alt-<?php echo $random_hash; ?> 
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Hello World!!!
This is simple text email message.
--PHP-alt-<?php echo $random_hash; ?> 
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
<h2>Hello World!</h2>
<p>This is something with <b>HTML</b> formatting.</p>
--PHP-alt-<?php echo $random_hash; ?>--
--PHP-mixed-<?php echo $random_hash; ?> 
Content-Type: application/zip; name="Doc1.pdf" 
Content-Transfer-Encoding: base64 
Content-Disposition: attachment 
<?php echo $attachment; ?>
--PHP-mixed-<?php echo $random_hash; ?>--
<?php
//copy current buffer contents into $message variable and delete current output buffer
$message = ob_get_clean();
//send the email
$mail_sent = @mail( $to, $subject, $message, $headers );
//if the message is sent successfully print "Mail sent". Otherwise print "Mail failed"
echo $mail_sent ? "Mail sent" : "Mail failed";
?> 

我不是要求你写我的代码，但也许你可以提供一些信息，或者让我知道是否可能。

编辑：

我的问题不是不使用smtp服务器，而是如何在不输入用户名和密码的情况下发送电子邮件。我知道，只有当发送电子邮件的请求来自我的服务器时，它才会起作用。