smtp and gpg-signature?

[Lars Wenderoth]

Hello guys!

I searched the web for some hours now, but I couldn't find a solution 
for my problem.. So I ask here...

The problem: I have to write a small MUA-portion, which has to send a 
gpg-signed mail. I have to use C to do this. My program is already able 
to send mails, which are multipart and contain the (detached) signature. 
But the recipient always reports: BAD signature... To make things a bit 
clearer: An example:

X-Mailer:LOMUA 0.0.1
Mime-Version: 1.0
From: xxx at yyy.com
To: xxx at yyy.com
Subject:signtest2
Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="trennzeile"
Message-Id: <id at yyy.com>
Date: Wed, 21 Jan 2004 00:27:37 +0100

--trennzeile
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

bla bla bla
--trennzeile
Content-Type: application/pgp-signature; name=outtext.txt.asc
Content-Description: Dies ist ein digital signierter Nachrichtenteil

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)

iD8DBQBADblqf87Sw9lmnEERAo2pAJ9taJIHIMQulhRBZIZYz8p15fWuJgCgkzK+
cKXjcZbIFSQHu5RG2F851EA=
=Ss11
-----END PGP SIGNATURE-----
--trennzeile--

The above example shows a part of the mail source as received at the 
recipient. The signature was generated using the part  "bla bla bla" as 
clear text entry... I also tried using the header part plus the text or 
even the boundary with the headers and the text to generate the 
signature.. But to no avail...

What I would like to know is: Which part of the mail code has to be 
signed? Or does anybody see any other problems?

Thanks for your help!