MsExchangeTeam has been posting information about the Exchange Server 2007 SP1. Now the topic was S/MIME.
S/MIME support for Exchange Outlook Web Access (OWA) was introduced in Exchange 2003. In Exchange 2007 SP1, we are adding S/MIME support back and making it more reliable and powerful. Below, is a short introduction to S/MIME and simple end-to-end steps for how to use S/MIME with OWA on Exchange Server 2007 SP1.
Read more at source: http://msexchangeteam.com/archive/2007/08/20/446760.aspx