test-email: a test message from Server › Health

Decided by the owner on 2026-10-13 (out of preflight); the sender is his
choice of 2026-10-16 ("Да, адрес годится"); mockups e92769f, e3b2501,
8f0ccf9, the route guard 75f97c9.

Card 09 on Health, in the right stack's static end (the left stack is
polled whole): one recipient and Send. HandleTestMessage (global role)
takes one address (validate.AccountEmail - no list, nothing that reads as
an option), at most ten an hour counted from the send log, writes the
message's send-log row first (store.InsertTestMessage: queued, the
hostname as domain, no application, no queue id), awaits its Message-ID
(logtail.AwaitMessageID) and hands it to sendmail as notifications go
(notify.Mailer.SendWithID: postmaster@ the hostname, signed by the local
socket with the key of the server's own name). The browser lands on the
row; the tailer gives it its queue id from cleanup's message-id= line
(src/cleanup/cleanup_message.c:639) and from then on its delivery lines
its status. Postfix refusing the hand-over removes the row; sendmail out
of time keeps it (postdrop may have queued it). The sweep closes a row
whose id was never seen once it is no longer awaited
(CloseUnmatchedTestMessages); an id awaited past ten minutes is not taken.

Reviewed for security before the commit (2026-10-17): no high or medium;
its three low findings are fixed in this commit (the unmatched row's
close, the awaited id's age, the timeout keeping the row) and the
security.md bullet says how the queue id is matched.

Tests: TestTestMessage (refusals, the row and the page, Postfix refusing,
the hourly ten), TestTestMessageTimeoutKeepsTheRow, TestTestMessageRows,
TestCloseUnmatchedTestMessages, TestAwaitedMessageID,
TestRunGivesTheTestMessageItsQueueID, TestHealthTestMessageCard; e2e sends
one to the sink: the row is sent with a long queue id, the sink has it
signed d=mail.e2e.test. go vet + go test (26 packages) and make e2e on the
test server for this tree.

Docs: help (word for word with the mockup), guide § Overview and Health,
architecture § Log tailer, security.md, CHANGELOG [Unreleased] § Added,
roadmap row done.

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

docs/security.md

@@ -686,6 +686,22 @@ deferred item from the roadmap.
   a dozen times a day at most by someone who flaps the zone; a domain's
   limits once a day; and no more than 60 messages leave in any hour whatever
   the rules arrive at.
+- **The test message is a form that sends mail** (test-email, `2.12.0`):
+  Server › Health sends one message to an address a global user types. It is
+  bounded as notifications are - the same `sendmail(1)` call, a fixed argument
+  list, the address after `--` - and further: the global role only; one
+  address, held by `validate.AccountEmail` (no list, no separator, nothing
+  that reads as an option, any public host); a fixed subject and body the
+  panel composes; ten an hour, counted from the send log whoever asks; the
+  origin check of every form. It is written to the Outbound log before it
+  goes, so each one is on record with its recipient and who asked is in the
+  panel's log. It cannot be made to say anything but the panel's own text,
+  and the sender is always `postmaster@` the hostname. Its row learns its
+  queue id from the head of cleanup's `message-id=` line; cleanup logs a
+  client's own Message-ID the same way, but the panel's is 96 random bits,
+  known to nobody before the line is read, taken once and not after ten
+  minutes - a message of someone else's cannot take the row (security
+  review, 2026-10-17).
 - **Whatever is submitted with sendmail(1) is signed as the server.** The
   signer's local socket, the whole of `non_smtpd_milters`, signs every
   message submitted locally with the key of the server's own name, whatever