fix(postfix): allow maillog under /data prefixes

postfix check fatally rejects maillog_file=/data/log/mail.log when
maillog_file_prefixes still default to /var,/dev/stdout — FATAL often never
reaches stderr or the rejected log path. Add /data to prefixes and pin the
postlog master service required for file logging.

Co-Authored-By: Composer <noreply@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

CHANGELOG.md

@@ -11,6 +11,11 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   into `/etc/postfix/tls-internal` as `root:root` before `postconf` /
   `postfix check`. Bind-mounted keys owned by the CI/host UID made
   `postfix check` fail and the container exit before supervisord started.
+- Postfix config: allow `maillog_file` under `/data` via
+  `maillog_file_prefixes=/var,/dev/stdout,/data`, and pin the `postlog`
+  master.cf service. After mail.log moved to `/data/log`, `postfix check`
+  fatally rejected the path (default prefixes are only `/var` and
+  `/dev/stdout`) and often left stderr/mail.log empty.
 
 ## [1.0.0] - 2026-08-09