I've managed to localize the issue to EFA by doing the following. I sent an S/MIME signed test message to two recipients, one inside the organization and one external to the organization. When comparing the two messages, there are differences.
The following is the (sanitized) message that passed through EFA (MUA -> MTA -> EFA -> Internet). Notice that after the initial address block (the first =C2=A0) there were two newlines inserted into the message. Also, the text/html block seems to have been 'reflowed' and the message lines are longer than the original message. While this doesn't change the message contents or its rendering, it does mess with the S/MIME (and DKIM) signature of the message, causing the recipient MUA to report that the message was tampered with:
Code: Select all
To: xxxxxxxxxx@gmail.com, Xxx Xxxxxx <xxx.xxxxxx@xxxxxxx-xxxxxx.com>
User-Agent: SOGoMail 4.0.4
MIME-Version: 1.0
Date: Tue, 20 Nov 2018 12:39:22 -0600
Subject: Test subject
Message-ID: <2b1e-5bf45500-f-f51ded0@206628022>
X-Forward: 10.3.24.8
From: Xxxxx Xxxxxx <xxxxx.xxxxxx@xxxxxxx-xxxxxx.com>
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1------
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Length: 216
Test message, test message, test message, test message
--
Xxxxx Xxxxxx
Xxxxxx Xxxxxx & Xxxxxxxxxx
999 X Xxxx Xx, Xxxxxxx, XX 99999
Phone=C2=A0999.999.9999
Fax=C2=A0999.999.9999
Website www.xxxxxxx-xxxxxx.com
=C2=A0
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1------
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Length: 616
<html>Test message, test message, test message, test message<br /><br />--<=
br /><span style=3D"font-size:14px;"><strong>Xxxxx Xxxxxx</strong></span><b=
r /><span style=3D"font-size:12px;"><span style=3D"color:#990000;"><strong>=
Xxxxxx Xxxxxx & Xxxxxxxxxx</strong></span><br />999 X Xxxx Xx, Xxxxxxx,=
XX 99999<br /><span style=3D"color:#990000;"><strong>Phone</strong></span>=
999.999.9999<br /><span style=3D"color:#990000;"><strong>Fax</strong>=
</span> 999.999.9999<br /><span style=3D"color:#990000;"><strong>Websi=
te</strong></span> www.xxxxxxx-xxxxxx.com</span><br /> </html>
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1--------
Code: Select all
To: xxxxxxxxxx@gmail.com, "Xxx Xxxxxx" <xxx.xxxxxx@xxxxxxx-xxxxxx.com>
User-Agent: SOGoMail 4.0.4
MIME-Version: 1.0
Date: Tue, 20 Nov 2018 12:39:22 -0600
Subject: Test subject
Message-ID: <2b1e-5bf45500-f-f51ded0@206628022>
X-Forward: 10.3.24.8
From: "Xxxxx Xxxxxx" <xxxxx.xxxxxx@xxxxxxx-xxxxxx.com>
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1------
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Length: 216
Test message, test message, test message, test message
--
Xxxxx Xxxxxx
Xxxxxx Xxxxxx & Xxxxxxxxxx
999 X Xxxx Xx, Xxxxxxx, XX 99999
Phone=C2=A0999.999.9999
Fax=C2=A0999.999.9999
Website www.xxxxxxx-xxxxxx.com
=C2=A0
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1------
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Length: 616
<html>Test message, test message, test message, test message<br /><br /=
>--<br /><span style=3D"font-size:14px;"><strong>Xxxxx Xxxxxx</strong><=
/span><br /><span style=3D"font-size:12px;"><span style=3D"color:#99000=
0;"><strong>Xxxxxx Xxxxxx & Xxxxxxxxxx</strong></span><br />999 X X=
xxx Xx, Xxxxxxx, XX 99999<br /><span style=3D"color:#990000;"><strong>P=
hone</strong></span> 999.999.9999<br /><span style=3D"color:#99000=
0;"><strong>Fax</strong></span> 999.999.9999<br /><span style=3D"c=
olor:#990000;"><strong>Website</strong></span> www.xxxxxxx-xxxxxx.com</=
span><br /> </html>
------=_=-_OpenGroupware_org_NGMime-11038-1542739162.591911-1--------