A multipart mail, with one empty part (eg. no text, spacing doesn't matter). Calling learn_ham or learn_spam in rspamc will cause the controller process to segfault

multipart_mail

Return-Path: <example@example.net>
Date: 29 Apr 2015 04:56:53 -0000
MIME-Version: 1.0
From: example@example.net
Subject: This is the subject
Content-Type: multipart/alternative;
 boundary="=_1ad00c4b74ff9921bb562f02b6e6df7a"
Message-ID: <mid1234@example.net>
To: example@example.net

--=_1ad00c4b74ff9921bb562f02b6e6df7a
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit


--=_1ad00c4b74ff9921bb562f02b6e6df7a
Content-Type: text/html; charset="ISO-8859-1"
Content-Transfer-Encoding: quoted-printable

<b>HTML part only. The previous part makes the controller process crash</b>

--=_1ad00c4b74ff9921bb562f02b6e6df7a--