Do you mean that you use apostrophes when they may not be grammatically
correct, such as
Cream 'n' sugar
Goin' to the store
?
You could turn off spelling (but then that won't help you with misspelled
words such as "apostrophe"), or you could add those special words to the
Autocorrect settings. In Outlook 2007:
On the Tools menu, click Options.
Click the Mail Format tab, and then click Editor Options.
Click Proofing, and then click AutoCorrect Options.
On the AutoCorrect tab, make sure the Replace text as you type check box is
selected.
In the Replace box, type a word or phrase that you often mistype or
misspell — for example, type usualy.
In the With box, type the correct spelling of the word — for example, type
usually.
Click Add.
If this doesn't work for you, please post back, and include the version of
Outlook and operating system you are using.