To configure this module, you need to go to `System parameters` and adjust `mail_restrict_follower_selection.domain` as you see fit. This restricts followers globally, if you want to restrict only the followers for a certain record type (or have different restrictions for different record types), create a parameter `mail_restrict_follower_selection.domain.$your_model`.
As an example, you could use `[('customer', '=', True)]` to allow only customers to be added as follower.
As an example, you could use `[('customer', '=', True)]` to allow only customers to be added as follower - this also is the default.
Note: This module won't change existing followers!