emailstop stops permanent all messages

The csv option emailstop stops the messages for users.

I have a Moodle with 10 test users.
The setting messagingallusers is active so all users can send messages to each other.
When the setting messagingallusers is inactive only the users in the same courses can send messages.
I uploaded a csv user list with emailstop=1 for some of these users in my test setting.
The option "Disable notifications" is active in the notification preferences of the correct users.
Now I uploaded the same csv user list with emailstop=0 for all users in my test setting.
Yes, the option "Disable notifications" is inactive in the notification preferences for all users.
But the users can't get messages where emailstop=1 disabled the notifications and emailstop=0 should reactivate them. They are not found by others when they are not in the same course.

My temporary solution is to put all users in an empty course. Now every user can be found in the user search in the messages.

Does the csv option emailstop set other parameters?