This was a common way to harvest 6-digit ICQ numbers back in the day. Hotmail, MSN etc. had expiring email addresses as well that you could register to reset the password to the ICQ number.
Yeah this has been a common attack since as early as I can remember. Company goes bust? Wait for their domain to expire then register/catch-all and start seeing what mail you get from websites to see where there’s accounts using that domain. Also plenty of more targeted methods too.
