KNode - 550 Message headers fail syntax check

Binary package hint: knode

I'm subscribed to Gmane using KNode v0.10.5 and Followup via Newsgroup works like a charm, however, when Replying via Email, I get an Undelivered Mail Returned to Sender message.

<email address hidden>: host lists.ubuntu.com[91.189.94.204] said: 550
    Message headers fail syntax check (in reply to end of DATA command)

Final-Recipient: rfc822; <email address hidden>
Original-Recipient: rfc822;<email address hidden>
Action: failed
Status: 5.0.0
Remote-MTA: dns; lists.ubuntu.com
Diagnostic-Code: smtp; 550 Message headers fail syntax check

Here's the full source as sent out by Knode:

From: Dax Solomon Umaming <email address hidden>
Subject: Re: 4G Memory Only Recognised 3.4G
To: Ubuntu user technical support,not for general discussions <email address hidden>
Reply-To: <email address hidden>
Date: Tue, 18 Dec 2007 12:23:13 +0800
References: <email address hidden> <email address hidden> <email address hidden>
Lines: 21
User-Agent: KNode/0.10.5
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7Bit

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQFHZ0s36Hw0ZHFcNUcRAh2iAJ4+gkP6zUeVj4fKHhbvG+qF2jR3BACgkoU1
Eb246xE1yNMDPwV2h/T+oY4=
=JBZK
-----END PGP SIGNATURE-----

Now it doesn't matter if I'm using my localhost (via Postfix), my SMTP server, my ISP's SMTP server, or Gmail's SMTP server... I'm still getting the said error.

I'm also subscribed on the Ubuntu-Users list. Anyone else experiencing this problem?