POP3: data after the end-of-body terminator is written into the retrieved message

When a POP3 server sends the end-of-body terminator and further data in the same read, curl writes the bytes after the terminator into the retrieved message's output file and still reports success. The PoC returns the message, its "." line, and then a second "+OK" response that answers no command; …

import socket, subprocess, threading, time, os
def srv(p):
    s = socket.socket(); s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.bind(("127.0.0.1", p)); s.listen(1); c, _ = s.accept(); b = b""
    c.sendall(b"+OK ready\r\n")
    while True:
        d = c.recv(4096)
        if not …