I duplicated a page with a form on it and forgot to activate all of the checkboxes for the send button. Now I have received an email from a prospect without ANY information in it, just my own noreply. Is there any way to retrieve the emailaddress? This could be a big client. 
Try checking your email headers, for anything with regards to a clue. If the client is willing to work with you, they would likely message again.
Let this also be a practice lesson, meanwhile. Imagine if you overlooked something for a big client, who then came and told you they have potential leads but no information or any way to know who they are and how to reach them.
Hello 
Unfortunately, if the submitted form contained no information and the email address was not collected, it will be impossible to retrieve it 
. However, you could check the time the email was sent by looking at its header (as suggested by @phoenix1386 ) to try to trace the activity of this visitor using an analytics tool like Google Analytics or Matomo, if you have one installed. That said, it is unlikely that this data will be precise enough to reliably identify the sender of this email…
I would put a notice on the site after you correct the problem and explain that the form may not have worked, and if anyone didn’t get a response to please inquire again.