I also received this email from Jacob some time ago:
I'm an engineer at Let's Encrypt. From our logs, it looks like you may be running an outdated kube-lego or cert-manager instance that is generating extremely high traffic to Let's Encrypt's servers. We've worked with Jetstack, the maintainers of kube-lego and cert-manager, to release an update to each of those packages. If you are using either of those tools, please update to the latest version, which will reduce the amount of traffic you are sending to Let's Encrypt.
I have (finally) made this change, I'm sorry it took so long. The kubernetes cluster is now running cert manager v0.4.0. However it seems cert-manager is has now been blocked with the "blocked due to ridiculously excessive traffic" error.
I saw this error myself on the cluster, but then I deleted the cert-manager pod and the error did not get redisplayed. However, all requests are failing with the error "Issuer letsencrypt not ready". I assume this means my IP has been blocked.
As different Let's Encrypt staff members may handle this issue at different times, I would suggest inviting the Let's Encrypt staff to comment on forum threads rather than providing users with a suggested individual contact.