Fresh kolab3 on Debian/Wheezy: local delivery is not staying local?

[Johannes Graumann]

Johannes Graumann wrote:

> Hello,
> 
> The Kolab3 System that is soon to replace my running 2.4 one currently has
> no mx record etc. set.
> This makes me suspect that the reason why locally triggered test mails
> (/etc/aliases has "root: me at mydomain.org") are not delivered is that
> postfix is not keeping such mails local but routing them out and they are
> thus currently not received.
> 
> Is that accurate? Can that postfix-behavior be changed?

I have since (with the off-list help of Paul Klos) made some headway into 
trouble shooting this. "/var/log/mail.info" reads for these emails:
> Feb 20 09:42:27 kolab postfix/smtp[2588]: A097D88041A:
> to=<root at kolab.<MYDOMAIN>.org>, relay=none, delay=0.14,
> delays=0.12/0.02/0/0, dsn=5.4.6, status=bounced (mail for
> kolab.<MYDOMAIN>.org loops back to myself)

Google seems to say that this has something to do with how "mydestinations" 
is defined in "/etc/postfix/main.cf", but in the kolab context that's an 
ldap lookup and I do not know how to tackle this.

Any pointers?

Sincerely, Joh