S/MIME: BAD HEADER SECTION, Duplicate header field: "MIME-Version"

[lantz]

The mail header appears not to be rendered correctly when sending S/MIME signed messages. The “MIME-Version” field is duplicated.

Please find one such mail header below (Kopano 11.0.0 nightly build):

Return-Path: <john.doe@example.com>
Received: from mx1.example.com (172.30.0.5:51158)
	by mail.example.com (kopano-dagent) with LMTP;
	Wed, 03 Feb 2021 22:19:14 +0100 (CET)
Received: from localhost (localhost [127.0.0.1])
	by mx1.example.com (Postfix) with ESMTP id C09AED01
	for <john.doe@example.com>; Wed,  3 Feb 2021 22:19:14 +0100 (CET)
Authentication-Results: mx1.example.com (amavisd-new);
	dkim=pass (1024-bit key) reason="pass (just generated, assumed good)"
	header.d=example.com
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=
	example.com; h=content-type:content-type:mime-version
	:message-id:x-mailer:mime-version:date:date:from:from:subject
	:subject:received:received:received; s=mail; t=1618987895; x=
	1614212346; bh=mpqBalG654gwroijgt2wLcUe+zGfmpxr3593hb0=; b=K
	h5dpx7owhWb2/kj6rpituh18674erthKjsTOByibmUZU3wrthYHBkAKAjSMGEYw/RSvmh
	eB++3eJBCmmL2z5hIZc/rkxTB9tyhtsfi7OsRQhqABXc0YsEypy0RW5JE/Umbx/
	A+n78Sl45641WTPJuHL6m/Vp38I2u6+I00SsHVy2fY=
X-Quarantine-ID: <4_Jb9OGeXdjM>
X-Virus-Scanned: amavisd-new at example.com
X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "MIME-Version"
Received: from mx1.example.com ([127.0.0.1])
	by localhost (mx1.example.com [127.0.0.1]) (amavisd-new, port 10024)
	with ESMTP id 4_Jb9OGeXdjM for <john.doe@example.com>;
	Wed,  3 Feb 2021 22:19:14 +0100 (CET)
Received: from mail.example.com (srv_mail-app_1.srv_backend [172.30.0.6])
	by mx1.example.com (Postfix) with ESMTP id E735FB7B
	for <john.doe@example.com>; Wed,  3 Feb 2021 22:19:13 +0100 (CET)
Received: by mail.example.com (kopano-spooler) with MAPI; Wed, 3 Feb
 2021 22:19:13 +0100
Subject: Test 6
From: "john doe" <john.doe@example.com>
To: "john doe" <john.doe@example.com>
Date: Wed, 3 Feb 2021 21:19:13 +0000
Mime-Version: 1.0
X-Priority: 3 (Normal)
X-Mailer: Kopano 11.0.0
Thread-Index: AYCeMThyjXNXkfetRO+pgVLjW2OUmQ==
Message-Id: <kcEE.lO0zsIhYSiWyD0eqHOLWdg.gJ4xOHL61gE@mail.example.com>
MIME-Version: 1.0
Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg="sha-256"; boundary="----F8865A14F82C11F6E1688D89A0BF3C07"

[fbartels]

Locking since reposted in https://forum.kopano.io/topic/3707/s-mime-bad-header-section-duplicate-header-field-mime-version-in-kopano-11-0-1