panel-notifications: findings of the technical and security reviews

Neither review (read-only agents, Opus and Fable, over 972a9f8..400aa76) has
a Critical finding. Both found the same serious one, and more:

- The notification about refused mail was built on what a rejected row says
  of itself. Its domain is the one in MAIL FROM, which the client typed and
  Postfix has not yet held against the login when the milter refuses: an
  application over its limit could have had the panel write a message per
  made-up domain, to another tenant's users among others. And the same
  status is written when an application is refused for its client address,
  which is no limit. Refusals are now counted by the domain the login is
  registered under, only for logins that exist and only while a limit is set
  on the login or its domain; one subject per sending domain. They are read
  through a partial index of their own (migration 0005): the query walked
  the whole send log every minute.
- Account and user e-mails were checked with the DMARC report validator,
  which refuses Gmail and the like - the owner's own kind of address. A new
  validate.AccountEmail accepts them and refuses a local part beginning "-".
- "Said" now means sent: what arises while nobody can be told, or while
  Postfix does not take the message, is told at a later check. Its ending
  with nobody left to tell is simply over.
- Two DNS checks must be 45 minutes apart as well as two: the last check
  before a restart and the first after it were minutes apart.
- The notifier's own mail waiting in the queue, and its bounce coming back
  to postmaster@ this server, are not the queue's subject. A listing cut at
  its size limit or with a line too long to read is no listing; postqueue -j
  gets 30 seconds.
- The tables must name the selector the panel shows, not only have the line.
- An a/mx lookup that did not answer inside the SPF check made the record
  "not authorising"; it is "cannot tell" now, for the pages too.
- A ceiling of 60 messages an hour; a pass stops between domains when the
  process is asked to stop; sendmail gets a WaitDelay; days are rounded as a
  person counts; a failed read of the switch shows it on, not off.

Recorded as accepted in security.md, with a roadmap candidate
(from-header-binding): an application can have a message signed as the
server's own name - or, as always, as another registered domain - by writing
it into the From: header, which nothing holds against the login.

Left as found: a recipient whose copy failed while another's went out is not
tried again; a certificate that lives under 14 days is reported at each
renewal.

On the test server, for this tree: go vet clean, go test ./... 23 packages
ok, make e2e ok (326 s).

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

internal/notify/text.go

@@ -53,9 +53,11 @@ func plain(s string, max int) string {
 	return string(b)
 }
 
-// days words a duration in whole days, the unit these messages count in.
+// days words a duration in days, the unit these messages count in, rounded
+// to the nearest: a certificate found thirteen days and twenty-three hours
+// from its end has fourteen days, not thirteen.
 func days(d time.Duration) string {
-	n := int(d.Hours() / 24)
+	n := int((d + 12*time.Hour) / (24 * time.Hour))
 	if n == 1 {
 		return "1 day"
 	}
@@ -70,8 +72,8 @@ func dnsProblem(hostname, domain string, faults []dnsFault, since time.Time) mes
 		lines[i] = f.Record + ": " + plain(f.Detail, 600)
 	}
 	return compose(hostname,
-		fmt.Sprintf("%s: %s no longer matches", domain, strings.Join(names, ", ")),
-		fmt.Sprintf("The DNS records of %s do not match what this server sends with. Two checks an hour apart found the same, the first at %s.", domain, stamp(since)),
+		fmt.Sprintf("%s: %s does not match", domain, strings.Join(names, ", ")),
+		fmt.Sprintf("The DNS records of %s do not match what this server sends with. Checks about an hour apart found the same, the first at %s.", domain, stamp(since)),
 		strings.Join(lines, "\n\n"),
 		fmt.Sprintf("Until the records are right, receivers may refuse mail from %s or file it as spam. The records to publish are in the panel under Outbound > Domains > %s.", domain, domain),
 		"One more message follows when the records match again.",
@@ -81,7 +83,7 @@ func dnsProblem(hostname, domain string, faults []dnsFault, since time.Time) mes
 func dnsCleared(hostname, domain string, since time.Time) message {
 	return compose(hostname,
 		fmt.Sprintf("%s: DNS records match again", domain),
-		fmt.Sprintf("The DNS records of %s match what this server sends with again; two checks an hour apart agree. They had not since %s.", domain, stamp(since)),
+		fmt.Sprintf("The DNS records of %s match what this server sends with again; checks about an hour apart agree. They had not since %s.", domain, stamp(since)),
 	)
 }
 
@@ -132,9 +134,9 @@ func queueCleared(hostname string, since time.Time) message {
 }
 
 func limitRefused(hostname string, r store.LimitRefusal) message {
-	who := "the domain " + r.Domain
-	if r.AppLogin != "" {
-		who = fmt.Sprintf("the application %s of %s", r.AppLogin, r.Domain)
+	who := fmt.Sprintf("the application %s of %s", strings.Join(r.Apps, ", "), r.Domain)
+	if len(r.Apps) > 1 {
+		who = fmt.Sprintf("the applications %s of %s", strings.Join(r.Apps, ", "), r.Domain)
 	}
 	count := "1 message"
 	if r.Count != 1 {
@@ -144,6 +146,6 @@ func limitRefused(hostname string, r store.LimitRefusal) message {
 		fmt.Sprintf("%s: a rate limit is refusing mail", r.Domain),
 		fmt.Sprintf("In the last 24 hours this server refused %s from %s under a level-2 rate limit, the first at %s. Refused mail is not queued: the application has to send it again.", count, who, stamp(r.First)),
 		fmt.Sprintf("If the volume is expected, raise the limit in the panel: Outbound > Domains > %s, on the domain or on the application. If it is not, the application is sending more than it should.", r.Domain),
-		"This limit is reported at most once a day.",
+		"Refusals of this domain's mail are reported at most once a day.",
 	)
 }