This message was sent with Enigmail to an Outlook with latest GPGOL:
Message-ID: <54D0840F.4020804@example.com>
Date: Tue, 03 Feb 2015 09:17:19 +0100
From: Someone <example@example.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
Thunderbird/31.4.0
MIME-Version: 1.0
To: "Someone else" <example2@example.com>
Subject: Re: Unencrypted
References: <54CF9A18.3030308@example.com>
<000301d03f04$eb1deb50$c159c1f0$@example.com> <54CFA908.5060609@example.com>
<002a01d03f08$9f0a8760$dd1f9620$@example.com>
In-Reply-To: <002a01d03f08$9f0a8760$dd1f9620$@example.com>
Content-Type: multipart/encrypted;
protocol="application/pgp-encrypted";
boundary="angLww5NBglDPam12536La7twpgL1rkk2"

This is an OpenPGP/MIME encrypted message (RFC 4880 and 3156)
--angLww5NBglDPam12536La7twpgL1rkk2
Content-Type: application/pgp-encrypted
Content-Description: PGP/MIME version identification

Version: 1

--angLww5NBglDPam12536La7twpgL1rkk2
Content-Type: application/octet-stream; name="encrypted.asc"
Content-Description: OpenPGP encrypted message
Content-Disposition: inline; filename="encrypted.asc"

-----BEGIN PGP MESSAGE-----
Version: GnuPG v1

<MUCH CRYPTO HERE>
-----END PGP MESSAGE-----

--angLww5NBglDPam12536La7twpgL1rkk2--

It yielded the following error. See screen shot.