public class EmailHelper
{
    const char emailSplitter = ',';    
    public static void Email(string toAddress, string fromAddress, string subject, string attachmentFile, string smtphost, int port)
    {
        string[] emails = toAddress.Split(new char[] { emailSplitter }, StringSplitOptions.RemoveEmptyEntries);
        if (emails.Length > 1)
        {
            foreach (var email in emails)
            {
                Email(email.Trim(), fromAddress, subject, attachmentFile, smtphost, port);
                Thread.Sleep(1000);
            }
            return;
        }
        MailMessage message = new MailMessage();
        message.To.Add(new MailAddress(toAddress));
        message.Subject = subject;
        message.From = new MailAddress(fromAddress);
        message.Body = subject;
        if (File.Exists(attachmentFile))
        {
            message.Attachments.Add(new Attachment(attachmentFile));
        }
        SmtpClient smtp = new SmtpClient(smtphost, port);
        smtp.Credentials = CredentialCache.DefaultNetworkCredentials;
        smtp.Send(message);
    }
}