If the private-public key pair, with its certificate, is stored on a smart card, a card reader must be properly attached to the mail user’s computer. The card reading device also requires software; the device and its software are supplied by the vendor from whom you purchase this equipment.
There are actually two parts to a system with card reading capabilities. One part is the hardware card reader and it's driver. The second part is the actual card, which is usually provided by a different vendor and requires drivers for reading the cards. Not all cards are supported. Refer to the Table 24–1 to see a list of the supported SmartCards (ActiveCard, now renamed ActiveIdentity, and NetSign).
When properly installed, a mail user inserts their smart card into the reading device when they want to create a digital signature for an outgoing message. After verification of their smart card password, the private key is accessible by Communications Express Mail to sign the message. See 24.2 Required Software and Hardware Components for information on supported smart cards and reading devices.
Libraries from the vendor of the smart card are required on the user’s computer. See 24.8 Key Access Libraries for the Client Machines for more information.