When accessing an Exchange 2003 server via IMAP, emails that were sent as text/plain (and ones that had no MIME encoding specified at all) get automatically converted to multipart/alternative with the original text/plain body and a text/html body. This is … stupid. It doesn't even bother to specify a monospaced font.
The new MIME part starts like this:
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Diso-8859-1">
<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
6.5.7654.12">
<TITLE>{{subject}}</TITLE>
</HEAD>
<BODY>
<!-- Converted from text/plain format -->
<BR>
<P><FONT SIZE=3D2>{{body}}
(All the "3D" stuff is quoted-printable encoding for an equals sign; there's nothing wrong on that front, surprisingly.)
How can I make this stop?
Gavin McTaggart responded to a similar question, albeit about Exchange 2007:
I haven't had a chance to test it yet. I don't really have any notion that the Exchange Management Shell indirectly referenced exists or will function with Exchange 2003, though.
Isn't this configured on the Message Format tab of the IMAP4 Virtual Server properties pages? I believe that sending the message in both Text and HTML formats is the default setting.