I have enabled all checkboxes for administrator in the email notifications screen (see attachment) (I am admin level). Then I have disabled all the checkboxes under my account/preferences for all email notifications (see the same attachment). Still I get an email on every change made to every issue. It seems the local user mail preferences are completely ignored when the global mail notification settings are enabled.

Note that this is also the case for other access levels but in the attachment picture it is only shown for admin level. This way our company is completely flooded with emails, and users cannot lower their email levels for themselves.