For those users who want to manually set their Notes 8.5.1 client to connect to Lotus Protector, you will need to specify the URL in a Notes ini setting for the Lotus Protector for Mail Security 2.5 server.
Note: This setting supports the use of an IP/HOSTNAME:PORT combination such as 188.8.131.52:4443 or protector.company.com:4443. The setting does not support the use of an http or https URL such as https://protector.company.com:4443.
Note: To locate the URL for the Protector server, see the Lotus Protector for Mail Security 2.5 documentation at https://www.ibm.com/developerworks/lotus/documentation/protector/mailsecurity.
Lotus Protector for Mail Security 2.5 Spam Protection features integrated into Notes/Domino 8.5.1
Lotus Protector Options on Domino Administrator desktop policy settings document
Lotus Notes/Domino 8.5.1