EMailing module for external users

Dear All,

I am new to Dolibarr and we want to provide access for external partner (external user) to manage email campaigns.
Although, rights are properly assigned by creating the group, assign rights and external user (partner),
the module shows access denied when accessed by the external user.
Obviously, modules for external user are defined and limited by standard, so we must override by the variable MAIN_MODULES_FOR_EXTERNAL (standard modules are facture,commande,contact,propal,projet,contrat,societe,ficheinter,expedition,agenda).
Unfortunately, the needed module name for EMailing cannot be found.
Can anyone please help by configuring the MAIN_MODULES_FOR_EXTERNAL correctly to allow external user to access the module emailing?
Thanks to all, have a nice evening,
Stefan