With amavisd-new-2.8.1-r1 I get my logs filled with this: amavisd[538]: (available_nameservers: No DNS servers available! amavisd[538]: rules: failed to run DKIM_ADSP_CUSTOM_LOW test, skipping: amavisd[538]: spf: lookup failed: available_nameservers: No DNS servers available! amavisd[538]: (available_nameservers: No DNS servers available!) amavisd[538]: rules: failed to run NO_DNS_FOR_FROM RBL test, skipping: amavisd[538]: plugin: eval failed: available_nameservers: No DNS servers available! Googling a bit I found: https://bz.apache.org/SpamAssassin/show_bug.cgi?id=7057 Suspecting the problem in Amavis to have the same root cause I decided to upgrade to 2.11. This solved the problem. Seems a version from 2013-06-28 is getting to old.
Recommend filing a stabilization request bug for the newer version of amavisd, then the old version can be dropped.
amavisd-new-2.11.0-r3 is now stable, so I think this can be closed. Please feel free to reopen if I'm wrong.