upstream-tls-verify: Verified TLS to an inbound domain's upstream

Owner, 2026-10-18: "Оба предложения делаем"; the mockup is c10cd78. The
security audit's M7: Required is Postfix's encrypt level, which checks no
certificate - it keeps the mail from a listener, not from one who answers
in the upstream's place.

- A fourth TLS mode, Verified, stored as Postfix's level secure (migration
  0014 rebuilds inbound_transports with the wider CHECK; schema 14) and
  written to the TLS policy map like the others. Postfix matches the
  certificate against the next hop's name (smtp_tls_secure_cert_match =
  nexthop, dot-nexthop, the default; postconf(5)), so Verified is refused
  for an upstream given by address (checkSecureHost).
- Postfix's SMTP client trusts Debian's ca-certificates bundle
  (smtp_tls_CAfile): Postfix trusts none by default (DEF_SMTP_TLS_CA_FILE
  "", DEF_TLS_APPEND_DEF_CA 0). The levels may and encrypt only log the
  verdict, so mail to recipients' MX is unchanged.
- The page: the select's fourth option, a help line under it, the lead
  "over verified TLS", the list's tag "verified"; Help word for word with
  the mockup; guide § Inbound relay, with a posttls-finger command to try
  an upstream first.

Tests: TestVerifiedTLSNeedsTheUpstreamsName, TestRenderInboundMapsSecure,
TestUpstreamTLSModeSecure; schema tests at 14. e2e
inbound_upstream_verified_tls: an address refused, a name saved as
"[sink]:25 secure" in tls_policy, the page says verified, the CA file set
and present, and posttls-finger -l secure with it calls the stand's
self-signed port 25 "Untrusted" (the stand has no TLS upstream). make e2e
(65 passed) and go vet + go test (26 packages) on the test server for this
tree. Tried against the live upstream from the 2.14.5 container:
mc-ent.mixfed.ru gives "Verified TLS connection established".

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

build/postfix-config.sh

@@ -297,9 +297,19 @@ postconf -e \
 	"local_transport=error:local mail delivery is disabled"
 
 # Outbound delivery: straight to the recipient MX, opportunistic TLS.
+# The client trusts the authorities Debian's ca-certificates ships, for an
+# inbound domain's upstream with Verified TLS (the "secure" level in the TLS
+# policy map, upstream-tls-verify): Postfix trusts none by default - the
+# *_tls_CAfile defaults are empty and tls_append_default_CA is "no" (Postfix
+# 3.10.13, src/global/mail_params.h, DEF_SMTP_TLS_CA_FILE,
+# DEF_TLS_APPEND_DEF_CA). The levels may and encrypt check nothing and only
+# log the verdict; mail to the recipients' MX is unchanged. The file is the
+# bundle update-ca-certificates writes (ca-certificates, installed in the
+# image), read by smtp(8) unchrooted (chroot is off below).
 postconf -e \
 	"smtp_tls_security_level=may" \
-	"smtp_tls_note_starttls_offer=yes"
+	"smtp_tls_note_starttls_offer=yes" \
+	"smtp_tls_CAfile=/etc/ssl/certs/ca-certificates.crt"
 
 # TLS server material shared by every inbound service. auth_only guarantees
 # credentials are never accepted before TLS is up on any port. Postfix 3.10.13,