I am not able to reproduce. Please advise an invalid email address to test.

i f we type in mail@ without a mailending it is validated true

Can not replicate

With a valid email address I have
<input type="email" inputmode="email" name="jform[contact_email]" class="form-control validate-email required valid form-control-success" id="jform_contact_email" value="" size="30" autocomplete="email" required="" aria-invalid="false">

With an invalid email address eg mail@ I have

<input type="email" inputmode="email" name="jform[contact_email]" class="form-control validate-email required form-control-danger invalid" id="jform_contact_email" value="" size="30" autocomplete="email" required="" aria-invalid="true">

Type in a.radtke@gjgjhh something behind the @

a.radtke@gjgjhh

that is a valid email address on internal networks

This should be closed as it is working correctly and the issue is that the user expected the validation to be different than it is

This not my main expertise, but I saw
https://help.xmatters.com/ondemand/trial/valid_email_format.htm

@wilsonge

This comes up every few years. It is perfectly valid to have an email address in the form user@localdomain
There is a reason there are standards and we shouldnt try to re-invent them

This should be closed for the reasons stated above