Here are the instructions for those who may also be having the same problem.
I hope they help you more than they have helped me.
Sending Messages in Plain Text
List of 10 items
. Open the tools menu (ALT-T)
. Cursor down to options and press enter
. Press control-tab three times to access the "send" property sheet
. Press the tab key until "Reply to messages using the format in which they
were sent." is located
. If this option is checked, use the spacebar to uncheck this check box.
This option should be unchecked.
. Press the tab key until the radio buttons are located
. Use the down arrow to select plain text
. Press the tab key three more times until the next set of radio buttons is
located
. Use the down arrow to select plain text
. Press enter to close the dialog and save the changes