Email suggestions while creating a tickets

I have encountered the following problem:
While creating a ticket (or even replying to ticket, commenting, etc.) there are mail suggestions.
These are no standard checkboxes, but when you start typing for example ‘use’, there is suggestion on the drop down list to add
It is really useful, however users might see email of other queues’ members and that is quite a problem.
Do you know any tips how to remove these suggestions or how to disable users from other Queues to pop up?
I saw no such right or config option to set.
Thanks in advance!

By default I believe RT autocompletes any user, you could look to use the callback in the share/html/Helpers/Autocomplete/Users ModifySuggestion to try and hide results though