>>Most probably you have enabled Word as the default editor. Try switching it off.
>>Select
>>. Tools/Options (menu)
>>. Mail Format (tab)
>>. uncheck the two boxes in the first section
>> . Use Microsoft Office Word...
>
>But, Word is good for the spelling. I just want to avoid this feature.

In Word, there is this nasty feature to automatically correct your spelling while you type. Perhaps if Word is used as the default editor for Outlook, changing the option in Word might help.

In Word 2003 (details may vary, I am translating from Spanish...), in this order:

Tools

Autocorrection (this is the third option from the bottom)

Automatically use suggestions from the spell checker (the last option at the bottom).

Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)