Limax PC Services
How to stop Outlook Express sending HTML
- select Tools on the Outlook Express menu bar

- select Options from the Tools drop-down menu

- select the Send tab (if it is not already selected)
- under Mail sending format select Plain Text
- under News sending format select Plain Text
- make sure Reply to messages using the format in which they were sent is not ticked
- press OK

The exact layout may vary with different versions of Outlook Express, so you may not see exactly the same display.
Similar options should exist in other email programs.