function verif() {
    if(document.getElementById("nom").value == "") {
        alert("Please enter a valid name!");
        document.getElementById("nom").focus();
        return false;
    }
    if(document.getElementById("email").value == "") {
        alert("Please enter a valid email address!");
        document.getElementById("email").focus();
        return false;
    } else {
        var mail = document.getElementById("email").value;
        var num_aro = 0;
        var pos_aro = 0;
        var num_pt = 0;
        var i;
        for(i=0; i<mail.length-1; i++) {
            if(mail.charAt(i)=="@") {
                num_aro++;
                pos_aro=i;
            }
        }
        for(i=pos_aro; i<mail.length-1; i++) {
            if(mail.charAt(i)==".")
                num_pt++;
        }
        if (num_aro!=1 || num_pt<1) {
            alert("Please enter a valid email address!\nRequired format : name@server.domain");
            document.getElementById("email").focus();
            return false;
        }
    }
    if(document.getElementById("tel").value == "") {
        alert("Please enter a valid telephone number!");
        document.getElementById("tel").focus();
        return false;
    }
    if(document.getElementById("email").value != "") {
    }
    if(document.getElementById("message").value == "") {
        alert("Please enter a valid message!");
        document.getElementById("message").focus();
        return false;
    }
    if(document.getElementById("spam").value == "") {
        alert("Anti-spam filter is required !");
        document.getElementById("spam").focus();
        return false;
    }
}