> I composed the message using Outlook 2007.  I'm not sure if Exchange put
in the line breaks or not.

I've just spent some time in RFC 2045, reading up on the rules.

The Content-Transfer-Encoding is the important header. In other words,
Exchange believed it was sending in the quoted-printable encoding; as it
happened, that encoding added nothing to that particular message. That means
those line breaks were already present in the plain text before the
quoted-printable conversion. If you weren't inserting them, then Outlook
might have done it.

A better test might be to send text including an equals sign, which
(according to the RFC) does require translation:
   The equation "2 + 2 = 4" has philosophical significance in George
Orwell's novel, "1984".

I switched on quoted-printable and sent that line to myself. The received
message had the equals sign encoded as =3D, although that was only visible
when I inspected the message source. (Outlook Express does translate that
correctly.)

Whether I got the soft line break depended on whether I told OE to limit my
lines or not, but it translated a received soft line break into a hard one.

Hal