ntp isn't a magical fix.You need a good selection of source servers, or local time sources for it to pick a steady reliable time to use.
Also, if the clock in your computer drifts too much, ntp will refuse to correct it or keep it in sync at all.
Quoting Frank Bonnet <f.bon...@esiee.fr>:
Hello I get this warning in dovecot.log the machine is running ntpd so this is a bit strange ...
