Hello @Fiona Kalinowska ,

To send Dunning Letters and Invoices to additional email addresses of the same customer:

1. Add the additional Contacts to the Contacts tab of the Customer profile screen.
2. On the Mailings and Settings screen, with cursor on Dunning Letter line, add the new Recipients to the bottom of the screen.
3. Repeat #2 for Invoices line of Mailings & Settings.

Laura

@Laura02 if I do it that way, dunnig letters would go to additional email adress I added in contacts and to standard email adress which is placed in the screen that you can see on the screenshot?
 

Hello, 

Please notice the highlighted Recipients field at the right side  of mailings tab is an option

1) to Add Recipients or

2) to Replace normal recipients with people listed in the second grid.

It is your choice to send to only new contacts OR to new contacts and standard email address.
Laura