sudden issue with spamassasin and dns?

[Greg Troxel <gdt%lexort.com@localhost>]

On a system with spamassasin, I am seeing

Jul 11 11:00:49 foo spamd[494]: plugin: eval failed: available_nameservers: No DNS servers available!

but in fact there is a local dns server (caching resolver) that appears
to be entirely ok whenever I query it with dig.

looking at a tcpdump of dns traffic, I don't see anything odd, even when
looking at an incoming message that threw that error.  I see a PTR query
for the address and then a few forward queries on the name that's in
From (perhaps helo) and that's it.

With no changed software, this feels like the system newly being in a
regime of running low on resources, but that doesn't really make sense.

This suddenly started happening yesterday.

It seems the rate of *.icu spam is huge, and I don't know if something
recently about that is newly overwhelming things, or if I had just been
blissfully unaware before.

I haven't tried to dig into the perl code yet.  It would seem best to
return 451 when spam filtering has a tempfail.

Is anybody else seeing this?