implement outgoing dmarc aggregate reporting

in smtpserver, we store dmarc evaluations (under the right conditions).
in dmarcdb, we periodically (hourly) send dmarc reports if there are
evaluations. for failed deliveries, we deliver the dsn quietly to a submailbox
of the postmaster mailbox.

this is on by default, but can be disabled in mox.conf.

dmarcrpt/parse_test.go

@@ -1,6 +1,7 @@
 package dmarcrpt
 
 import (
+	"encoding/xml"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -62,6 +63,7 @@ const reportExample = `<?xml version="1.0" encoding="UTF-8" ?>
 
 func TestParseReport(t *testing.T) {
 	var expect = &Feedback{
+		XMLName: xml.Name{Local: "feedback"},
 		ReportMetadata: ReportMetadata{
 			OrgName:          "google.com",
 			Email:            "noreply-dmarc-support@google.com",
@@ -126,7 +128,7 @@ func TestParseMessageReport(t *testing.T) {
 	dir := filepath.FromSlash("../testdata/dmarc-reports")
 	files, err := os.ReadDir(dir)
 	if err != nil {
-		t.Fatalf("listing dmarc report emails: %s", err)
+		t.Fatalf("listing dmarc aggregate report emails: %s", err)
 	}
 
 	for _, file := range files {