请问怎么获取pop3邮件的中有几封新邮件？

LIST [msg]
Arguments:
a message-number (optional), which, if present, may NOT
refer to a message ed as deleted
Restrictions:
may only be given in the TRANSACTION state
Possible Responses:
+OK scan listing follows
-ERR no such message
Examples:
C: LIST
S: +OK 2 messages (320 octets)
S: 1 120
S: 2 200
S: .
...
C: LIST 2
S: +OK 2 200
...
C: LIST 3
S: -ERR no such message, only 2 messages in maildrop