Details of filled in fields

Hi,

I have a problem with a received email: the email address of the sender is not in the output email but does has to be filled in on the form on the website. This means that I cannot reply to this person…
The problem is I activated ‘Use HTML’. I unchecked it again so the problem is solved. But how can I consult what the sender has filled in in the form on the website? So I can recover the email address. Is this possible?

https://www.ads-software.com/plugins/contact-form-7/