<script>
function ctrl() {
var f = document.mailing
if (f.blob.value == "") {
alert("E' necessario inserire un indirizzo E-Mail valido.")
f.blob.focus();
return false;
}
else
{
alert("OK");
}
}
</script>

<form method="POST" name="mailing" enctype="multipart/form-data" action="upload.asp">
<p align="center"><font color="#000080" size="2" face="Arial">

File: </font><input type="file" name="blob" size=30>

<input type="button" name="Enter" value="Aggiungi" onclick="return ctrl();">
</form>