Yesterday, I got a DKIM-signed message from Super User with the subject "Check out the Super User Weekly Newsletter". It has been eons since I used the account and, yep, I couldn't even recover the password for the account by providing the email address that the message was sent to.
The URLs in the email (e.g. one starts with https://stackexchange.com/email/unsubscribe-newsletter/) are all 404s. But the content looks legitimate.
Is this the result of some botched internal testing?