Regarding zen.spamhaus.org

[Kannabismus]

I got lot of of message about turning on and off RBL (I use zen.spamhaus only). It comes every 20-60 minutes.
Internet connection is stable. How could I diagnose and fix this?

Messages are:
install_if_changed: updating /var/qmail/supervise/smtp/run..........ok

and

This message is to notify you that /var/qmail/supervise/smtp/run has been altered. The difference between the new file and the old one is:

18a19
> >       -r zen.spamhaus.org \
and so on

Thank you.

[matt]

That's telling you that DNS resolution for zen.spamhaus is failing for some reason. Use a DNS client (like dig) and figure out why. Often, installing a local dnscache on your mail server will resolve the problem. Or cease using that RBL. 

[rainer_d]

spamhaus has a limit on the number of free queries they allow.
Once your IP is above that threshold (e.g. because you are an ISP with a couple of thousand accounts), they just lock you out.
I recommend Barracuda RBL: http://www.barracudacentral.org/rbl
and Heise IX RBL: ix.dnsbl.manitu.net (if you are in Germany/Europe - list may or may not be useful in your part of the world)