For millennia, humans have used various methods to hide information in transit, validate the sender, and authenticate the message. Now one method for handling all three has been developed and is becoming widely used—Secure Multi-Purpose Internet Mail. There are several stages to bootstrapping, composing, sending, and receiving signed or encrypted e-mail using S/MIME. This article covers  the details, problems, and potential solutions as it walks through a typical S/MIME scenario: two users sending signed and/or encrypted e-mail to each other from two different Active Directory forests and different certificate authority chains using Microsoft® Office Outlook® 2007.