I just tried sending a message with a yes/no button on it to a POP account. It ended up with these headers:

X-MimeOLE: Produced By Microsoft Exchange V6.0.6249.0
content-class: urn:content-classes:message
MIME-Version: 1.0
Content-Type: text/plain;
        charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Subject: Test message
Date: Fri, 1 Nov 2002 12:04:29 +1300
Message-ID: <5FA042F680739D44951B00FED8BE1A7D05DF0C@exchange.server.FQ
+DN.here>
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
Thread-Topic: Test message
Thread-Index: AcKBMk8DSPh8eUOZSCenOuSDeutYJA==
[download]

TNEF is apparently Transport Neutral Encoding Format and the X-MS- prefix implies Microsoft proprietary extensions, but I can't see anything in these headers that shouts out 'Yes/No Voting Button'. :-(