Two of the four ipv4 nameservers for gnu.org are broken. By those odds, I would expect anything up to 50% of any mail you receive via ipv4 to bounce.
Which has nothing to do with anything. I gave you some hints in this direction the last time you mentioned you were getting bounces but maybe you didn't see my posting due to your problem with your nameservers? Uhm, it has nothing to do with "nameservers". Just the fact that this is the _only_ list in the whole world that sends bounces like this should tell you something. Just the fact that multiple people have complained about bounces should tell you something.