Lead Note visibility

Summary:

We have a functionality where we add notes via a groovy within Lead to the notes object and it is only visible to the user who have added the note.

We want to make sure who has access to the lead should have access to all the note records as well.

We have kept the VisibilityCode attribute to External. - users are not able to check each others quote.

But when the set the VisibilityCode attribute to Internal - users are able to check each others quote.

Wanted to understand how the VisibilityCode value is related to Notes visiblity.