Going back to study homepage here https://privacystudy.cs.princeton.edu/ there is another update, now from the lead investigator, that includes the following paragraph:

"Second, our team is prioritizing a possible one-time follow-up email to recipients, identifying the academic study and recommending that they disregard the prior email. If that is feasible, and if experts in the email operator community agree with the proposal, we will send the follow-up emails as expeditiously as possible."

Did this study send automated emails in such volume that they can't work out how to send an apology without triggering spam protections? Or did they send email and not record it? What is he saying here?