After you add the group name to the address field, press F9 to expand the group list name and view all of the members. Then remove one or more names before sending the invitation or message.
The certificate information is included in a person's contact record on the Certificates tab.
The easiest way to add certificates for a person is to ask them to send you a message that is signed with either their Internet certificate or their IBM(R) Lotus(R) Notes(R) certified public key. Then, when you receive the message, add the name to your contacts. If you already have a record for the person, you will have the opportunity to update the record.
Another way to include certificate information for a contact record is to copy a name from the server's directory to your contacts. You do this from the Select Addresses dialog box. Click an address field in a new document (a message for example). Select a name and then click Copy. Note however, if the record already exists in your contacts, no action is taken.