A user could signup with an incorrect email
Another user could signup with an address ("1 rue de la castillere") !
Use per-input validation https://marmelab.com/react-admin/doc/3.19/CreateEdit.html#validation
Since your comment here was front-end related only, should I add backend-validation as well?
At the moment we don't do validation on the backend. To do it correctly, we should probably use ShEx (see https://github.com/assemblee-virtuelle/semapps/issues/795). But for Pods this may be more difficult, as different applications may have different validation rules for the same types of data. I first wanted to include ShEx validation in the NLNet grant request, but I put this for later as I don't know if there is an easy solution.
So for now the idea would be to do all validation on the frontend. In the future, we could even use ShEx to validate data on the frontend.