Just a small hint (this page serves as a reminder for me mainly) for using Thunderbird as default mail reader with KDE4. You may run the
systemsettings command (or click on it in the KDE panel), select the mail client entry and type the following line for thunderbird:
/usr/bin/thunderbird -compose "subject=%s,cc=%c,to=%t,attachment=%A"
Works like a charm here. Reference doc is at https://developer.mozilla.org/en/Command_Line_Options and also by letting the mouse over the text box where you have to pass that text.
Typically OpenOffice.org which uses on Mandriva 2010.1 by default the
xdg-menu entry for the default mail reader just does the right thing when ask to send by mail the current document.