Because normal email is not secure.
888.762.7932
"In our line of work, we know email's just not secure. With our investigators working cases all over the world, the privacy of their email messages is absolutely paramount. Now, we can exchange secure email messages with anyone, anywhere—as long as we have an Internet connection... Its way cool."
Don Criswell, Criswell Investigation Agency, San Francisco (also in Spokane, Paris and The Hague)