<?php	
$mail=$_POST["mail"];	
if($mail)
{						 
 $stremail=$mail;
$result=ereg("^[^@ ]+@[^@ ]+\.[^@ ]+$",$stremail,$trashed);
if(!$result){
echo "SLECHT";
}	 
else
{
echo"GOED";
}  
}
?>
<form action="test.php" method="post">

<input type="text" name="mail" size="40" maxlength="256">
<input type="submit" value="check">
</form>