It’s fairly well documented that you can restrict users from emailing certain groups if you change the readers field on the group to specified users/groups. That works great (in later releases).
You can’t however say the same about iNotes. When a user addresses a memo to a “restricted” group in iNotes, they get the following error:
If the user clicks on “Use Name Anyway” the mail is successfully sent. Not great.
This will apparently be fixed in Domino R8.5.2 FP2 and R8.5.3.