How to keep Mail from encoding messages with the old charset=windows-1252? A few of my colleagues using Mail, and myself, are unwillingly
and without any knowledge of this misbehaviour,
sending messages encoded with a charset of windows-1252:

Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: quoted-printable
[...]
Mime-Version: 1.0 (Mac OS X Mail 7.2 \(1874\))
X-Mailer: Apple Mail (2.1874)


I see the same problem coming from many different versions of Mail.
This is a serious problem since for some anti-spam and anti-virus filters, messages encoded with
this historical coding are identified as coming from SPAM sources or viruses.

Of course, I found an easy way to choose the format used to encode one message.
But this function doesn't scale for people dealing with tenths or hundreds of messages.

How is it possible to avoid sending messages with this historical and
malware symptomatic format?
How is it possible to definetly and easily choose the format used for
all sent messages?
As far as I know, the only way to guarantee the encoding is to make sure every message includes an Unicode dingbat (e.g. in the sig).  This will ensure that the message goes out as UTF-8.  Dingbats are in the Unicode 2700 range, e.g. ✈ .  You need to add this from the Character Viewer, not by just changing to a "dingbat" font, which may not be Unicode.