package mailparser

import (
	"net/mail"
	"strings"
)

// Only the topmost Return-Path counts: it is added by the final delivering
// mailserver; lower ones stem from earlier hops or the sender.
func returnPath(h mail.Header) string {
	values := h["Return-Path"]
	if len(values) == 0 {
		return ""
	}
	v := strings.TrimSpace(values[0])
	if v == "" || v == "<>" {
		return ""
	}
	a, err := mail.ParseAddress(v)
	if err != nil {
		return ""
	}
	return strings.ToLower(strings.TrimSpace(a.Address))
}