TidTelnet to send SMTP Emails...freezing

Dear Experts,

We have a huge list of email adresses of our customers and we need to find out which email adresses are still valid and which are not before sending out informations.

to do this, the idea is to connect to the SMTP server, pass the RCPT TO command and depending on the answer of the server we will then know if the email is valid or not.

The problemi i have, using the Telnet Indy component, is that many times it freezes or it gets a message "gracefully disconnected" . I've put an AntiFreeze component but it doesn't help.

I'm not sure i'm using the correct way to read the result of the connection, or i should use some kind of event handler before trying to read the answer of the server...could you help?

the code i'm testing is the following (replaced original values with 'bogus')

 telnet.Host := 'mailhost.domain.com';
 Adomain := 'user@domain.com';
 telnet.Port := 25;
 telnet.ConnectTimeout := 2000;
 telnet.ReadTimeout := 2000;

 try
       telnet.Connect;
       telnet.SendCmd('ehlo bogus.net');
       telnet.SendCmd('mail from: <mailings@bogus.net>');
       telnet.SendCmd('rcpt to: <' + Adomain + '>');
       telnet.SendCmd('quit');
       memo1.Lines.Add(IntToStr(telnet.LastCmdResult.NumericCode));
       memo1.Lines.Add(telnet.LastCmdResult.Text.CommaText);
          if (telnet.LastCmdResult.NumericCode = 250) then
             begin
              label3.Caption := 'Email is valid';
             end;
          if (telnet.LastCmdResult.NumericCode = 550) then
             begin
              label3.Caption := 'Email is NOT valid';
             end;
          if (telnet.LastCmdResult.NumericCode <> 250) and
             (telnet.LastCmdResult.NumericCode <> 550) then
             begin
               label3.Caption := 'Error code: ' + IntToStr(telnet.LastCmdResult.NumericCode);
             end;
       telnet.Disconnect(False);

 except
  on E : Exception do
    Begin
     memo1.Lines.Add(E.ClassName + ' : ' + E.Message);
         label3.Caption := 'Error code: ' + E.Message;
     telnet.Disconnect(True);
    end;
 end;