Walter Embalsado has this to add to yesterday's tip:

Another option is what I usually employ - either:

I don't put anything on the To: CC: or BC: until after I run the Spell checker or  I intentionally misspell any word within the body.
Both are good methods and the first has saved me many a time. Note that it only works on new mail, unless you like deleting and replacing the addresses. The second requires spellcheck on send enabled, which is a good idea anyway, even if you use Word for spell check as you type, since using File, Send to in other applications doesn't use Word as the editor. It also spellchecks your subject field.