This Redmine plugin will activate the “Hide my email address” preference by default.
In your redmine directory, execute the following:
ruby script/plugin install git://github.com/splendeo/redmine_hide_emails_by_default.git rake db:migrate_plugins RAILS_ENV=production
(Change environment to test or development if needed)
Re-start your web server.
From then on, all new users will have the “Hide my email address” set to true by default.