Small issues with using socket to connect to the POP3 server

Use SOCKET to connect to the POP3 server. I use encoding. ASCII for character encoding.
1. send command user <username> \ r \ n
+ OK
2. send command pass <password> \ r \ n
+ OK
3. Send command list \ r \ n
At this time, if you immediately go to socket. Receive (bytes), sometimes you can only get + OK \ r \ n,
However, you cannot obtain complete data packets. Although you can use socket. available to determine the data volume, you can still obtain incorrect data.
Therefore, after sending the LIST Command, we recommend that you use thread. Sleep (100) to delay and then receive socket data.
When you use RETR <n> \ r \ n to receive mail content, it is best to set up a delay.

The POP3 server has a time-out limit. A Noop command should be issued in seconds to maintain the connection.