Конфигурирование зашифрованной электронной почты в Outlook 2010

"Encrypted email" is a very general term. Outlook supports X.509 (S/MIME), for OpenPGP you need plugins.

It does usually not make sense to use the same certificate for several users. Doesn't look very professional to the outside world neither. If that is your aim then it may be easier not to use any crypto on the clients but use a crypto mail gateway instead. That way it should even be easily possible to support S/MIME and OpenPGP simultaneously (without having to care about Outlook's limited capabilities).

A key distribution infrastructure exists for OpenPGP but not for S/MIME.