$von = $_POST['von']; $email = $_POST['email']; $betreff = $_POST['betreff']; $nachricht = $_POST['nachricht']; $fertig = $_POST['fertig'];

function checkEmail( $email )
{
    $nonascii      = "\x80-\xff";    
    $nqtext        = "[^\\\\$nonascii\015\012\"]";
    $qchar         = "\\\\[^$nonascii]";
    $normuser      = '[a-zA-Z0-9][a-zA-Z0-9_.-]*';
    $quotedstring  = "\"(?:$nqtext|$qchar)+\"";
    $user_part     = "(?:$normuser|$quotedstring)";
    $dom_mainpart  = '[a-zA-Z0-9][a-zA-Z0-9._-]*\\.';
    $dom_subpart   = '(?:[a-zA-Z0-9][a-zA-Z0-9._-]*\\.)*';
    $dom_tldpart   = '[a-zA-Z]{2,5}';
    $domain_part   = "$dom_subpart$dom_mainpart$dom_tldpart";
    $pattern       = "$user_part\@$domain_part";
    
    if (!preg_match( "/$pattern$/", $email ))
    {
        return FALSE;
    }
    else
    {
        return TRUE;
    }