static boolean sendEmail(str toAddress, str theSubject, str body, str fromAddress)
{
    SysEmailParameters parameters = SysEmailParameters::find();

    System.Net.Mail.SmtpClient            mailClient;
    System.Net.Mail.MailMessage           mailMessage;
    System.Net.Mail.MailAddress           mailFrom;
    System.Net.Mail.MailAddress           mailTo;
    System.Net.Mail.MailAddressCollection mailToCollection;
    System.Net.Mail.MailAddressCollection mailCCCollection;
    System.Net.Mail.AttachmentCollection  mailAttachementCollection;
    System.Net.Mail.Attachment            mailAttachment;
    System.Net.NetworkCredential          mailCredentials;

    System.Exception                      e;
    List            toList;
    ListEnumerator  le;


    SMTPRelayServerName mailServer;
    SMTPPortNumber mailPortNumber;
    SMTPUserName mailUserName;
    SMTPPassword mailPassword;

    InteropPermission interopPermission;
    ;

    try
    {
        interopPermission = new InteropPermission(InteropKind::ComInterop);
        interopPermission.assert();

        if (parameters.SMTPRelayServerName)
        {
            mailServer = parameters.SMTPRelayServerName;
        }
        else
        {
            mailServer = parameters.SMTPServerIPAddress;
        }

        mailPortNumber  = parameters.SMTPPortNumber;
        mailUserName    = parameters.SMTPUserName;
        mailPassword    = SysEmailParameters::password();
        mailCredentials = new System.Net.NetworkCredential(mailUserName,mailPassword);


        mailClient = new System.Net.Mail.SmtpClient(mailServer, mailPortNumber);
        mailFrom = new System.Net.Mail.MailAddress(parameters.SMTPUserName); //fromAddress);

        toList = strSplit(toAddress,';');
        le = toList.getEnumerator();
        le.moveNext();

        mailTo  = new System.Net.Mail.MailAddress(strLTrim(strRTrim(le.current())));
        mailMessage = new System.Net.Mail.MailMessage(mailFrom, mailTo);

        mailToCollection = mailMessage.get_To();
        while(le.moveNext())
        {
            mailToCollection.Add(strLTrim(strRTrim(le.current())));
        }


        mailMessage.set_From(mailFrom);
        mailMessage.set_ReplyTo(mailFrom);
        mailMessage.set_Priority(System.Net.Mail.MailPriority::High);
        mailMessage.set_Subject(theSubject);
        mailMessage.set_IsBodyHtml(true);
        mailMessage.set_Body(body);

        if(parameters.TIDUsingSSLorTSL)
        {
            mailClient.set_EnableSsl(true);
            mailClient.set_UseDefaultCredentials(false);
            mailClient.set_Credentials(mailCredentials);
        }
        else
        {
            mailClient.set_EnableSsl(false);
        }


        mailClient.Send(mailMessage);

        mailMessage.Dispose();

        CodeAccessPermission::revertAssert();

        //info("Email has been send.");
    }
    catch (Exception::CLRError)
    {
        e = ClrInterop::getLastException();
        while (e)
        {
            info(e.get_Message());
            e = e.get_InnerException();
        }
        CodeAccessPermission::revertAssert();
        return false;
    }
}

source : my senior’s code