The MIME boundary seperators are generated wrong. Notice that the boundary generated has 004e0db68a, but the first boundary is 003d075f9e. Editing this in my mbox after receiving the messed up email (I use nmh/mh-e), I can decode the email.
I am unsure how to determine the version of SWA.
MIME-Version: 1.0
Content-Type: multipart/related;
boundary="scalix-part-004e0db68a=_02"
--scalix-part-003d075f9e=_02
Content-Type: multipart/alternative;
boundary="2_0_125_17bd474MHTML_=_01"
--2_0_125_17bd474MHTML_=_01
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline