How do I create two public email adrresses with same recipient but in different domains?

Citadel supports multiple email addresses for a user, and they may be in different domains. To do this, you must have the MX records for all domains pointing to your Citadel server, and then identify the domains to Citadel: Contacts -- Local users -- identify the user to be edited, and select "Edit".

Select the "Internet email addresses" tab. You can add as many addresses as you want here, as long as they are unique and in domains you operate. The first address is the one that will be used by default for outbound messages.