Fix (reverse dns) should be in progress. Once it's working all the undelivered mail should go through. It's only been affecting some ISPs' mailservers, not others.
Broken: roadrunner, comcast, cox, aol...
The big three (google, yahoo, hotmail) look like they've been working.
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...” (blade runner)
“Who are you?” “A friend. I'm here to prevent you from making a mistake.” “You have no idea what I'm doing here, friend.” “In specific terms, no, but I swore an oath to protect the world...” (continuum)
“It's a goal you won't understand until later. Your job is to make sure he doesn't achieve the goal.” (bsg)