While administrators have access to all data in LUXletter, editors have only limited access to guarantee privacy in a multiclient installation.
Newsletters need a configuration record where sender information is stored. There is also a selection with available sites for this configuration. Take care that your editor has reading access to a root page in a site, otherwise the site will not be shown. In addition, reading access to root pages with sites is also needed to see relevant newsletters in list view.
This means, that if an editor needs access to all LUXletter data, ensure that this editor has reading access to all root pages.
Take care that your editors have reading access to pages where relevant records are stored (sys_category and fe_groups). Only available records are shown if a new newsletter record will be created.
In addition, available newsletters in options are only listed for editors if there is reading access to those pages.