test.cs

using System.Net.Mail;

public static class SmtpMail
{
    /// <summary>
    /// Sends an email with the specified recipient, subject, body, and attachment.
    /// </summary>
    /// <param name="recipient">The recipient's email address.</param>
    /// <param name="subject">The subject of the email.</param>
    /// <param name="body">The body content of the email.</param>
    /// <param name="attachment">The email attachment.</param>
    public static void Send(string recipient, string subject, string body, Attachment attachment)
    {
        // Create a new email message with sender and recipient details.
        MailMessage emailMessage = new MailMessage("sender@yourdomain.com", recipient)
        {
            Subject = subject,            // Set the email subject.
            IsBodyHtml = false,           // Specify that the body is plain text (not HTML).
            Body = body                   // Set the email body content.
        };

        // Add the specified attachment to the email.
        emailMessage.Attachments.Add(attachment);

        // Configure and send the email using an SMTP client.
        using (SmtpClient client = new SmtpClient())
        {
            client.Host = "smtp.yourprovider.com";                              
            client.UseDefaultCredentials = false;                              
            client.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;           
            client.Credentials = new System.Net.NetworkCredential("username", "password"); 
            client.Port = 587;                                                 
            client.EnableSsl = true;                                           

            // Send the email.
            client.Send(emailMessage);
        }
    }
}