Create the rule
Open Settings, then Mail and Rules. Select Add a new rule and give it a clear name, such as Invoice forwarding.
Choose conditions
A condition identifies messages to process. Use Sender is for a supplier address, or Subject includes with “Invoice”. Several conditions refine the rule: a message must meet the selected conditions.
Choose the action
Select Redirect to and enter the accountant’s email address. Redirecting keeps the original sender visible.
Exceptions and rule order
Add an exception only when needed, for example to exclude credit notes. Keep Stop processing more rules enabled if no other rule should process the message; disable it when another rule must still file it.