// Package courier implements various couriers for delivering messages.
package courier

// Courier delivers mail to a single recipient.
// It is implemented by different couriers, for both local and remote
// recipients.
type Courier interface {
	// Deliver mail to a recipient. Return the error (if any), and whether it
	// is permanent (true) or transient (false).
	Deliver(from string, to string, data []byte) (error, bool)
}