[kim-aa]

Чего то вы не то прочли

вот из приведенного вами RFC

TOP msg n

Arguments:
a message-number (required) which may NOT refer to to a
message marked as deleted, and a non-negative number
of lines (required)

Restrictions:
may only be given in the TRANSACTION state

Discussion:
If the POP3 server issues a positive response, then the
response given is multi-line. After the initial +OK, the
POP3 server sends the headers of the message, the blank
line separating the headers from the body, and then the
number of lines of the indicated message's body, being
careful to byte-stuff the termination character (as with
all multi-line responses).

Note that if the number of lines requested by the POP3
client is greater than than the number of lines in the
body, then the POP3 server sends the entire message.

Possible Responses:
+OK top of message follows
-ERR no such message

Examples:
C: TOP 1 10
S: +OK

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У вас проблема что нет ответов
+OK

вы бы ручками к серверу прицепились через telnet 110
И команды поотдавали опять же ручками