Header was:
From example.user@t-online.de Wed Oct 09 10:21:57 2002
Return-path: <example.user@t-online.de>
Envelope-to: user@test.example.com Delivery-date: Wed, 09 Oct 2002 10:21:57 +0200 Received: ===hidden===
To: user@example.com
Subject: Re: Your mail
From: example.user@t-online.de
Date: Wed, 09 Oct 2002 10:23:52 +0200 (CEST)
Message-ID: <23758295.8767v7i6u675@webmail.t-online.de>
In-Reply-To: <E17yzpu-00060u-00@test>
References: <E17yzpu-00060u-00@test>
X-Mailer: T-Online WebMail 2.05
X-Complaints-To: abuse#webmail@t-online.com
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
X-Sender: ===hidden===@t-dialin.net
Got it running by my self.
The first line was the problem.

my $firstline=1;

while (<STDIN>) {
        if (!($firstline)) {
                push(@mail, $_);
        }
        $firstline=0;
}
$msg = Mail::Message->read(\@mail);

$sender = $msg->sender;
$replyto = Mail::Address->parse($msg->head->get('Reply-To'));
if ($replyto) {
        $sender =$replyto;
}
$subject = $msg->subject;

if($msg->isMultipart) {
        $summary = $msg->body->preamble;

        $summary .= "Number of attachments: ".scalar $msg->body->parts
+('ACTIVE')."\n\n";
        my $number =0;
        foreach my $part ($msg->body->parts) {
                $number++;
                $summary .= "======== Attachment ".$number." Type: ".$
+part->get('Content-Type')." =========\n";
# Attachment handling
                if ($part->get('Content-Type') eq "text/plain" ) {
                        $summary .= $part->decoded."\n";
                }
                $summary .= "=========================================
+=================\n\n";
        }
        $summary .= $msg->body->epilogue;
}
else {
        $summary = $msg->decoded;
}
$summary.="\nMail from: ".$sender->format();
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