RE: External Users Ben Williams 3.Jul.15 06:30 AM Lotus Notes Administration 9.0Windows
You'd have to add them to your LDAP server or create a new LDAP directory for them. Once in LDAP they will authenticate like anyone else. You will though have a licensing implication that you need to consider as these users are now the same as an internal employee.
You add people to your LDAP assuming you're using Domino as an LDAP directory using a Notes client. You do not need to register a Notes ID, they only need to be person documents with a name, Short name/UID and email. The email can be fictional but must be populated. You can set the "mail system" on the person document to be "other" which allows you to enter an email address.