Windows Mail comes with the default language for spellchecking partly
set to English, but not enough to work. To fix this, click on Tools, then
Spelling, then the triangle to the right of English, then some other
language, then Apply, then the triangle again, then English, then Apply.
You may also want to click on the box before Always check spelling
before sending; leave it with a check mark if you want this. Click on
Apply again, then OK.