This test makes use of DNSOverride and the new verifying milter to
ensure that signatures can be verified properly.
It doesn't test the actual interaction with the public DNS, but
getting that kind of test to work on arbitrary platforms might be more
trouble than it's worth.
I note that the DNSOverride only works as long as testkey.dns is a
single line, which is fine for ed25519, but maybe not for RSA.
Daniel Kahn Gillmor