Plesk update stopped
xinetd service, but didn't start it afterwards.
Linux kernel sometimes keeps sockets opened for some time after the program exits. It prevents another program (the next instance of
xinetd) from binding to them, so
xinetd can simply terminate.
Add delay (
sleep 1; command) in the
/etc/init.d/xinetd file between
root@mail:~# grep -A3 " restart" /etc/init.d/xinetd restart|force-reload) $0 stop sleep 1; $0 start