function validateEmail(emailId) {
    var emailRegEx = /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i;
    var email = document.getElementById(emailId);

    if (emailRegEx.test(email.value) && email.value.length > 0)
        return true;
    else {
        alert("Impossible d'envoyer le formulaire. \n Adresse e-mail non valide.");
        email.focus();
        return false;
    }
}