Looks like this does not work!

Nov 19 15:02:18 lt postfix/smtp[22046]: BB1A395: to=<users@lists.roundcube.net>, relay=ext-mx02.kolabsys.com[94.230.208.222]:25, delay=0.16, delays=0.06/0.01/0.07/0.02, dsn=5.7.1, status=bounced (host ext-mx02.kolabsys.com[94.230.208.222] said: 553 5.7.1 <users@lists.roundcube.net>: Sender address rejected: not logged in (in reply to RCPT TO command))