Free email (S/MIME) Certificate from Actalis
Follow this link and enter the email address for which you need the certificate:
https://extrassl.actalis.it/portal/uapub/freemail?lang=en
You will receive an email (first in Italian, with and English translation below!):

Copy and paste the verification code into the web page that was shown after you submitted the email address.
You will then be emailed the certificate, and shown the password required to access it on the web page. Save the password somewhere secure in case you need to re-install the certificate another time.
Double-click the certificate file to open the Windows Certificate import wizard:


Allow the wizard to determine where to store the certificate.
To check the certificate and/or export the public key search the Start menu for 'Manage user certificates'. It should be installed in Personal > Certificates.