Problem of SMTP & Winsock

I use the following steps to send my messages
Winsock.Connect - HELO - MAIL - RCPT-DATA - QUIT - Winsock.Close
when next time I send another message and try to repeat the sequence above, It took me forever to get response ( 220 - SMTP ready) from SMTP server after call Winsock.connect and stock there.

If I remove Command "QUIT" (Winsock.Connect - HELO - MAIL - RCPT-DATA - Winsock.Close) from the steps, it works fine. Does anyone know why?

I had the error event (sckTimedout) after I run my program for long time, the error occur right after "HELO" once a while. I am wondering if this was caused by the SMTP server timeout due to I did not use "QUIT" to discoonect the SMTP transimmision channel.

I am confused by the difference between "QUIT" and Winsock.close. When Winsock Close event occur after Send "QUIT" command, but if I just use Winsock.Close method, never fire the Close Event.

I also have another question about command "NOOP". Can use NOOP anywhere? If I use NOOP, it means SMTP never be disconnected by timeout due to no data transmission?

Yiping