I have tried sending them in all three making the adjustment via tools/options/mail format, but I also noticed there is a check box if you go addressbook/(pick a name)/properties/name and in the lower left hand corner is a ck box for sending E-Mail in plain text only, I don't know which one takes presidence. The return messages are kind of vague, something to the effect of not being able to open a winmail.dat attachment, or it just wasn't there.