Send billing-related emails to Billing contact only (if exists)
If a Billing contact has been defined, any billing related mail should only go to that person.
Especially with bigger companies, but more and more with the smaller companies aswell, they have a dedicated address for billing / invoicing related E-mail.
We or they define it as such in the system, but to their (and our) surprise the main contact is still receiving all billing E-mail aswell and they find this very annoying as well as that it doesn't help clarity or streamlining payment of the invoices.
When a billing contact has been defined (or another contact that has billing ticked aswell), that contact should get billing related issues, and the main contact shouldn't anymore.