“It appears that a sizeable number of companies configured DKIM TXT records in 2007 and never changed them.”
Debian’s 2008 OpenSSL bug cut the key space to a few tens of thousands of keys. In 2024, 855 DKIM records in the Tranco top million still used them, including hosts at Cisco, Oracle, 1Password and partner domains for CrowdStrike and Dropbox. That let anyone forge signed mail for those domains and pass DMARC. Cakemail’s security address bounced, and Seznam’s security team didn’t believe the report. Nothing in DKIM forces key rotation, so nobody rotated.