Importation of third part certificate with Outlook 2007

Since the 2007 version of Outlook, the importation of the certificates received along with signed e-mails is no longer automatic. They have to be manually imported in the addresses book:

"When Outlook users receive the signed message, they right-click the user's name on the From line and click Add to Contacts. The address information and the certificate are saved in the Outlook user's contacts list."