sender check: the reply names no other domain (L8); which key signs, tested (stage 2)

L8: a From: line naming another sender of the server was refused with
"it names another sender of this server, <domain>" - a confirmation, to
whoever tries names, that the domain is hosted here. The reason now stops
before the domain; the line as written stays in the reply (the client's own
text) and on the refused message's page (header_from). Unit test: the reason
of every refusal names none of the server's other domains; e2e: the reason
of each sender-check refusal does not contain other.e2e.test.

Which key OpenDKIM signs with (owner, 2026-10-13): the check and OpenDKIM
read From: with two parsers, and their agreement was argued, never run.
internal/milter/testdata/from-lines-passed.txt holds the lines the check
passes for an application - bare and bracketed, quoted names with a comma,
escaped quotes and an address inside, an extension, three encoded charsets,
two folded lines, comments (nested too), a stranger's address in the name -
as Go-quoted strings with {domain}. The unit test wants each passed; the new
e2e case passed_from_lines_signed_for_their_domain_only sends each as app1
and wants every DKIM signature at the sink to be for the sender domain,
with one valid. All fifteen were. "(the shop) a@domain" - a comment before
the address, valid RFC 5322 - is refused by the check ("it must be one
address"); strict, not a hole, so it is not in the file. Groups are refused
too.

Audit plan lines ticked (two) with what was found, CHANGELOG [Unreleased],
roadmap 21/62.
Evidence on the test server for this tree (with a618ffb): go vet clean, go
test ./... 23 packages ok, make e2e exit 0 - the new case passed in 4 s.

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

internal/milter/sender.go

@@ -331,7 +331,11 @@ func (s *senderSession) judge() (shown, why string, err error) {
 			return shown, "", fmt.Errorf("signing table: %w", err)
 		}
 		if signs {
-			return printable(raw), "it names another sender of this server, " + d, nil
+			// Which one is not said: the reply would confirm to whoever
+			// tries names that another tenant sends from this server (audit
+			// 2026-10-12, L8). The line as written is in the reply and on
+			// the refused message's page.
+			return printable(raw), "it names another sender of this server", nil
 		}
 	}
 	// And one that needs to know nothing of OpenDKIM's parser: outside quoted