<script language="javascript">
function kontrol(myForm) {
if(/^\w+([\.-]?\w+)*@\w+([\.-]?w+*(\.\w{2,3})+$/.test(myForm.eposta.value)) {
return(true)
}
alert("Geçersiz E-Posta Adresi")
return(false)
}
</script>

<form action="liste.php" onSubmit="return kontrol(this)">
E-Posta Adresiniz<br>
<input type="text" name="eposta"><br>
<input type="submit" value="Gönder">
</form>