Version:           1.5.2 (using KDE KDE 3.1.2)
Installed from:    SuSE RPMs
OS:          Linux

Using the builtin inline OpenPGP feature for sending emails with attachments generates email messages, which cannot be decrypted successfully with other mails, i.e. MS Outlook with plugin and some versions of Mozilla/Enigmail.

The problem has been identified as the name="encrypted message part" parameter of the mime header Content-Type of the main text. Excerpt of a not properly working real sample:

------- BEGIN
...
Subject: SAMPLE
User-Agent: KMail/1.5.2
MIME-Version: 1.0
Content-Type: Multipart/Mixed;
  boundary="Boundary-00=_/8OI/Dsh4vZhfr7"
Message-Id: <200307251050.12464@VAIO.int.whitestein.ch>


--Boundary-00=_/8OI/Dsh4vZhfr7
Content-Type: text/plain;
  charset="us-ascii";
  name="encrypted message part"
Content-Transfer-Encoding: 7bit

-----BEGIN PGP MESSAGE-----
Version: GnuPG v1.2.2-rc1-SuSE (GNU/Linux)

hQQOA7RtcHPOD76AEBAAh+yAfosqA9N66XnzAsGB59lt0LyvA7P2sQvk2uIacZeD
...
=/xXP
-----END PGP MESSAGE-----

--Boundary-00=_/8OI/Dsh4vZhfr7
Content-Type: application/pgp-encrypted;
  name="test.txt.pgp"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="test.txt.pgp"

hQQOA7RtcHPOD76AEA/8C8tEx99kNy4iXsv+9avMDoW7w+KufxG37NLIphcC2xKqF1bQHAj4On+g
...
Bkwt1WQXwa0/LNC8KjapkIg=

--Boundary-00=_/8OI/Dsh4vZhfr7--

------- END


After removing name="encrypted message part" (and the leading ;), the same message can be successfully decrypted by the receiver.

NOTE: PGP/MIME is in this case not an option, because it is not supported by the receiving mail client.

NOTE: The problem remains even if the attachment is not encrypted.

NOTE: I will gladly send you working and not working samples, if you provide me your public key.

FIX: do not label the encrypted main text as "encrypted message part" in the mime tree.


Regards
- tom