Enter button trigger to send email without completion

This is my code:

<label> Requester E-mail 
    [email* your-email placeholder "The e-mail address you used to register to our service"] </label>

[group group-1]
<label> Requester Name and Surname 
    [text* your-name] </label>
<label> Patient Name 
    [text* patient-name] </label>
<label> Patient Surname 
    [text* patient-surname] </label>
<label> Patient Age 
    [text* patient-age] </label>
<label> Patient Location 
    [text* patient-location placeholder "Hotel/B&B/Other - Street - Number - City"] </label>

<label> Patient Phone
[tel* Numero placeholder "+34512345678"]  </label>

<label> Symptoms
    [text* symptoms] </label>

<label> Notes
    [textarea notes] </label>

<strong>[checkbox* checkbox-813 "I have read and accept the processing of personal data." ]</strong>
<a href="https://wwww.medicalservicesinitaly.com/privacy-policy/">Privacy Policy</a><br />

[submit "Invia"]
 [/group]

I wanted to enable the form submition only if the first step is correct, but if a user fill the email first conditional field with a not valid content and press enter the form get submitted with all empty fields. The send button is hidden, how it’s possible?
How can I managed this?