Sorry about the late response, your post fell through the cracks.
The best way is to use the 'email' plugin, not the 'receipt' plugin (which is basically deprecated, it's only there for legacy reasons). With the 'email' plugin, if you have multiple recipients, each recipient receives an individual email, with none of the other recipients in the headers. So if there's 3 recipients, we send 3 distinct emails to those 3 addresses, as separate SMTP transactions.
-- hugh