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 `[('category_id.name', '=', 'Employees')]` to allow
only contacts with 'Employees' tag to be added as follower - this also is
the default.

Note: This module won't change existing followers!