Outlook 2007 – MS Exchange Server

Just recently upgraded to MS Outlook 2007 on the MS Exchange Server. Spell check is running on my sender’s messages when I reply. If there is a string of replies, it is stopping each time. How can this be avoided? I have searched under the Spelling & Grammar and can find no where to turn this function off. I want to be able to spell check my OWN messages, but not that of any senders.