Creating Multiple Email Addresses in Contact for Invoice Contact

What is the correct format for creating multiple email addresses in Customer Contact? Example: xx@yy.xxx comma space next email address, or semi colon, with space or without, etc.

We set up a Contact with a Role of Invoice Contact and use Email as a distribution method.  In many cases the Customer is requesting that invoices be sent to multiple email addresses.  Please advise correct format that should be used when we need to create multiple addresses.