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)