Not trying to be a jerk or anyting, maybe some spell checkers are better then others? This was with Outlook spell check.
FYI, it was grammar checking and not spell checking that would catch those errors. It is under your language tools of your word processor/MUA/whatever software you are running.
Never substitute human eyes for computer logic in language checking.
For the same reason 'right' was used when you wanted the homonym 'write'.
No big deal.
PS, Firefox web browser has Spellchecking capabilities