I think the answer depends on how the ezine folded and whether it assigned any rights or assets to a third party, such as a general assignment for the benefit of creditors. You need more info. If it was my story, I'd "reply" to the notice email they sent, thank them for the information, and say I'll assume the NA first publishing rights have reverted to me unless I hear back from them otherwise in seven days by reply email. And I'd send the email via receipt acknowledgment, high priority. But that's just me. A literary rights lawyer might have better advice.