No, není to zrovna vymoženost, spíš postranní efekt na UNIXových strojích (viz fetchmail/pop3.c):
Though the POP RFCs don't document this fact, on almost every POP3 server I know of messages are marked "seen" only at the time the OK response to a RETR is issued.
This means we can use TOP to fetch the message without setting its seen flag. This is good! It means that if the protocol exchange craps out during the message, it will still be marked `unseen' on the server. (Exception: in early 1999 SpryNet's POP3 servers were reported to mark messages seen on a TOP fetch.)