About Spell Check in OWA
In the Exchange 2013 version of Outlook Web Access (OWA), the spell check function has been removed by Microsoft. Spell checking/proofing is now only supported by the web browser.
Cobweb recommends that Exchange 2013 customers use Internet Explorer 10 when using OWA. This browser is currently only available on Windows 7 or above.
This is mentioned in the Supported Browsers section of the What's New for Outlook Web App in Exchange 2013 article that can be found by clicking here.