from-header-binding: what the reviews had left as found, and address extensions

The owner on the three things the reviews' commit left as found: can they be
fixed? They can.

- Downtime that crossed a UTC midnight was all booked on the day of the
  restart: it is cut at the midnights between (byDay).
- A message with the null envelope sender - a bounce an application writes
  itself - left a refusal row without a domain, which no domain
  administrator would see: the row takes the domain the login is bound to.
- A log read again after an unclean stop counted its deferrals again: while
  the tailer catches up, a warning no later than the last one counted is
  passed over. The mark is kept to the fraction of a second the log gives.

And on the check being stricter than Postfix for an address with an
extension (invoices+x@ passed in the envelope, was refused in the header):
it makes Postfix's second try now, the address without its extension.
recipient_delimiter was the distribution's default; it is set in
postfix-config.sh, since the check depends on it. e2e sends one through.

Test server, this tree: go vet ok, go test 23 packages ok, make e2e ok (339 s).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/logtail/logtail.go

@@ -153,7 +153,7 @@ func Run(ctx context.Context, path string, st StatusStore, retention RetentionDa
 			journal.handle(line, now, catchingUp)
 		}
 		if deferred != nil {
-			deferred.handle(line, now)
+			deferred.handle(line, now, catchingUp)
 		}
 		keeper.add(line, now, catchingUp)
 		queueID, recipient, status, ok := parseDelivery(line)

internal/logtail/sendercheck.go

@@ -33,9 +33,11 @@ import (
 // "milter unix:<socket>: can't read … reply packet header" (Postfix's
 // milter8.c; not seen on the stand).
 
-// SenderCheckStore is where the count goes. *store.Store satisfies it.
+// SenderCheckStore is where the count goes, and where the time of the last
+// counted line is kept. *store.Store satisfies it.
 type SenderCheckStore interface {
 	AddSenderCheckDeferred(at time.Time, n int64) error
+	SenderCheckDeferredAt() (time.Time, error)
 }
 
 // SenderCheck turns the counting on: the store and the socket Postfix was
@@ -60,10 +62,22 @@ type deferredCounter struct {
 	// listening, and a reply that did not come.
 	connect, broken string
 	failed          map[string]bool // smtpd pid -> its current client was counted already
+	// last is the time of the latest line counted, by this run or an earlier
+	// one. While the tailer catches up after a start it may be reading lines
+	// it had read before an unclean stop; a warning no later than this was
+	// counted then. mail.log's stamps are whole seconds, so a warning of the
+	// very second of the last one counted can be passed over - once, at a
+	// restart - which is the cheaper mistake than counting a stretch twice.
+	last time.Time
 }
 
 func newDeferredCounter(sc *SenderCheck) *deferredCounter {
+	last, err := sc.Store.SenderCheckDeferredAt()
+	if err != nil {
+		log.Printf("log-tailer: sender check statistics: %v", err)
+	}
 	return &deferredCounter{
+		last:    last,
 		st:      sc.Store,
 		connect: "warning: connect to Milter service unix:" + sc.Socket + ":",
 		broken:  "warning: milter unix:" + sc.Socket + ":",
@@ -71,8 +85,9 @@ func newDeferredCounter(sc *SenderCheck) *deferredCounter {
 	}
 }
 
-// handle looks at one mail.log line.
-func (c *deferredCounter) handle(line string, now time.Time) {
+// handle looks at one mail.log line. catchingUp is true until the tailer has
+// read to the end of the log for the first time.
+func (c *deferredCounter) handle(line string, now time.Time, catchingUp bool) {
 	at, rest := lineTime(line, now)
 	m := smtpdLineRe.FindStringSubmatch(rest)
 	if m == nil {
@@ -94,6 +109,12 @@ func (c *deferredCounter) handle(line string, now time.Time) {
 			c.failed = make(map[string]bool)
 		}
 		c.failed[pid] = true
+		if catchingUp && !at.After(c.last) {
+			return
+		}
+		if at.After(c.last) {
+			c.last = at
+		}
 		if err := c.st.AddSenderCheckDeferred(at, 1); err != nil {
 			log.Printf("log-tailer: sender check statistics: %v", err)
 		}

internal/logtail/sendercheck_test.go

@@ -7,13 +7,19 @@ import (
 
 type deferredStore struct {
 	days map[string]int64
+	last time.Time
 }
 
+func (d *deferredStore) SenderCheckDeferredAt() (time.Time, error) { return d.last, nil }
+
 func (d *deferredStore) AddSenderCheckDeferred(at time.Time, n int64) error {
 	if d.days == nil {
 		d.days = make(map[string]int64)
 	}
 	d.days[at.UTC().Format("2006-01-02")] += n
+	if at.After(d.last) {
+		d.last = at
+	}
 	return nil
 }
 
@@ -65,9 +71,41 @@ func TestDeferredCounter(t *testing.T) {
 		// cleanup that writes it.
 		`2026-10-13T00:01:00.000000+00:00 mail postfix/cleanup[1195]: B6B484831946: milter-reject: END-OF-MESSAGE from unknown[10.77.0.1]: 5.7.1 From: director@other.e2e.test - not an address this application sends as; from=<alerts@sender.e2e.test> to=<rcpt@sink.e2e.test> proto=ESMTP helo=<x>`,
 	} {
-		c.handle(line, now)
+		c.handle(line, now, false)
 	}
 	if len(st.days) != 2 || st.days["2026-10-12"] != 1 || st.days["2026-10-13"] != 1 {
 		t.Fatalf("deferred per day = %v, want one on each of the two days", st.days)
 	}
 }
+
+// After an unclean stop the tailer reads again some lines it had read. What
+// was counted then is not counted now; what was written while the panel was
+// down - the very lines this count exists for - is.
+func TestDeferredCounterDoesNotCountALogReadAgain(t *testing.T) {
+	st := &deferredStore{}
+	now := time.Date(2026, 10, 12, 18, 0, 0, 0, time.UTC)
+	outage := func(pid, at string) []string {
+		return []string{
+			at + `0+00:00 mail postfix/smtpd[` + pid + `]: connect from unknown[10.77.0.1]`,
+			at + `1+00:00 mail postfix/smtpd[` + pid + `]: warning: connect to Milter service unix:/run/selfpost/sender.sock: Connection refused`,
+		}
+	}
+	first := append(outage("11", "2026-10-12T16:00:00.00000"), outage("12", "2026-10-12T16:00:05.00000")...)
+
+	c := newDeferredCounter(&SenderCheck{Store: st, Socket: "/run/selfpost/sender.sock"})
+	for _, line := range first {
+		c.handle(line, now, false)
+	}
+	if st.days["2026-10-12"] != 2 {
+		t.Fatalf("first run counted %d, want 2", st.days["2026-10-12"])
+	}
+
+	// A new run: the same lines again, then what the outage added.
+	c = newDeferredCounter(&SenderCheck{Store: st, Socket: "/run/selfpost/sender.sock"})
+	for _, line := range append(first, outage("13", "2026-10-12T16:00:09.00000")...) {
+		c.handle(line, now, true)
+	}
+	if st.days["2026-10-12"] != 3 {
+		t.Fatalf("after the restart the day has %d, want 3", st.days["2026-10-12"])
+	}
+}