public class EmailProgram
{
    /// <summary>
    /// call this Method to send an Email with attachments
    /// </summary>
    /// <param name="emailFrom">From EmailID</param>
    /// <param name="emailTo">To Email ID</param>
    /// <param name="emailCC">CC Email ID</param>
    /// <param name="emailBCC">BCC Email ID</param>
    /// <param name="subject">Subject</param>
    /// <param name="body">Body</param>
    /// <param name="IsBodyHtml">EmailBodyFormat(Default It is false, If It is true EmailBody should in HTML Format)</param>
    /// <param name="attachmentPath">Attachment File Path</param>
    /// <returns>If sends successfully returns True otherwise False</returns>
    public String SendMail(String emailFrom,
    String emailTo,
    String emailCC,
    String emailBCC,
    String subject,
    String body,
    ArrayList attachments,
    bool IsBodyHtml)
    {
        try
        {
            bool ValidateFromEmailAddress = ValidateEmailAddress(emailFrom);
            if (ValidateFromEmailAddress == false)
                return "Invalid From Email Address: " + emailFrom;
            bool ValidateToEmailAddress = ValidateEmailAddress(emailTo);
            if (ValidateToEmailAddress == false)
                return "Invalid To Email Address: " + emailTo;
            MailAddress mailFrom = new MailAddress(emailFrom);
            MailAddress mailTo = new MailAddress(emailTo);
            MailMessage mailMessage = new MailMessage(mailFrom, mailTo);
            mailMessage.Subject = subject;
            mailMessage.Body = body;
            mailMessage.IsBodyHtml = IsBodyHtml;
            if (!String.IsNullOrEmpty(emailCC))
            {
                bool ValidateCCEmailAddress = ValidateEmailAddress(emailCC);
                if (ValidateCCEmailAddress == false)
                    return "Invalid CC Email Address: " + emailCC;

                mailMessage.CC.Add(emailCC);
            }
            if (!String.IsNullOrEmpty(emailBCC))
            {
                bool ValidateBCCEmailAddress = ValidateEmailAddress(emailBCC);
                if (ValidateBCCEmailAddress == false)
                    return "Invalid BCC Email Address: " + emailBCC;
                mailMessage.Bcc.Add(emailBCC);
            }

            foreach (string attach in attachments)
            {
                Attachment attached = new Attachment(attach, MediaTypeNames.Application.Octet);
                mailMessage.Attachments.Add(attached);
            }
            String strSMTPServer = ConfigurationSettings.AppSettings.Get("SMTPServer");
            SmtpClient smtpClient = new SmtpClient(strSMTPServer);
            //smtpClient.Credentials = new NetworkCredential("UserName", "Password");//if credentials needed 
            smtpClient.UseDefaultCredentials = true;
            if (mailMessage != null)
            {
                smtpClient.Send(mailMessage);
            }
            return "Message sent to " + emailTo + " at " + DateTime.Now.ToString() + ".";

        }
        catch (Exception ex)
        {
            return ex.Message.ToString();
        }
    }
    /// <summary>
    /// check email address is valid or not 
    /// </summary>
    /// <param name="emailAddress">email address to validate</param>
    /// <returns>True if email address is valid</returns>
    public bool ValidateEmailAddress(string emailAddress)
    {
        try
        {
            string TextToValidate = emailAddress;
            Regex expression = new Regex(@"\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}");

            if (expression.IsMatch(TextToValidate))
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        catch (Exception)
        {
            throw;
        }
    }
}