I have an application that requires an email alert to be sent to specific corporate users when the proper conditions exist.

Environment:
Corporate enterprise network
Exchange Server
MS Office 2003
Over 14,000 users in AD
VERY tight security

My application is installed with full-trust privileges.

Would it be best to use CDO (Collaboration Data Objects) to send information directly through Exchange?

Or should I use PIA (Primary Interop Assemblies) to automate MS Outlook?

Keep in mind that the action needs to be transparent to the user (i.e. If using outlook, I don't want to desensitize users to security issues by constantly exposing them to email warnings.).