Here's the text of the notification e-mail:
We recently discovered a bug in the Let's Encrypt certificate authority code, described here:
Unfortunately, this means we need to revoke the certificates that were affected by this bug, which includes one or more of your certificates. To avoid disruption, you'll need to renew and replace your affected certificate(s) by Wednesday, March 4, 2020. We sincerely apologize for the issue.
If you're not able to renew your certificate by March 4, the date we are required to revoke these certificates, visitors to your site will see security warnings until you do renew the certificate. Your ACME client documentation should explain how to renew.
If you are using Certbot, the command to renew is:
certbot renew --force-renewalIf you need help, please visit our community support forum: Revoking certain certificates on March 4
Please search thoroughly for a solution before you post a new question. Let's Encrypt staff will help our community try to answer unresolved questions as quickly as possible.
Your affected certificate(s), listed by serial number and domain names:
(certs)
[Or, if the list is very long, the e-mail has this text instead:]
You can find which of your certificates are affected by downloading the list of affected certificates at Download affected certificate serials for 2020.02.29 CAA Rechecking Incident - Let's Encrypt and searching for lines starting with account IDs:
(account IDs)