[acdha]

They at least were not historically archived. This came up during the Hunter Biden laptop investigation where people were able to verify some of the messages only because the Gmail key was archived in many places because that service is so popular. I’m not aware of anyone making a comprehensive archive but I’d be unsurprised if someone did based on news like that.

https://github.com/robertdavidgraham/hunter-dkim#but-gmails-...

EDIT: this one exists but is incomplete: https://archive.prove.email/about