Each time Jiglu receives a non-delivery notification when trying to send email to a user it adds to a score. If the score gets high enough because messages are consistently rejected then email to the user will be deactivated.
If a user logs on after this happens then they will be given the option to try again to send email to their address to reactivate it or to switch to a new one. If they don't log in then Jiglu can be set to automatically deactivate the entire account after a certain number of days have passed. This can be helpful for ensuring the security of the system so old accounts can't be accessed.
On the User workflow settings category there is a Deactivate user if email deactivated for setting, which determines after how many days since messages started bouncing the user account should be deactivated. After an account is deactivated it will require intervention by a system administrator should it be required to reactivate it.
Users can also be automatically deactivated when they haven't logged in for a while - see How can I see and deactivate users that haven't logged in to the system recently?