archivmail/pkg/mailparser/forwarded.go

package mailparser

import (
	"net/mail"
	"strings"
)

// Display only: Return-Path is sender-controlled and must never drive access decisions.
func ForwardedVia(pm *ParsedMail) string {
	if pm == nil {
		return ""
	}
	rp := normalizeAddress(pm.ReturnPath)
	if rp == "" || rp == normalizeAddress(pm.From) {
		return ""
	}
	for _, list := range [][]string{pm.To, pm.CC, pm.BCC, pm.DeliveryAddresses} {
		for _, a := range list {
			if normalizeAddress(a) == rp {
				return rp
			}
		}
	}
	return ""
}

func normalizeAddress(s string) string {
	s = strings.TrimSpace(s)
	if s == "" || s == "<>" {
		return ""
	}
	if a, err := mail.ParseAddress(s); err == nil {
		return strings.ToLower(strings.TrimSpace(a.Address))
	}
	return strings.ToLower(strings.Trim(s, "<>"))
}