feat(mail): 支持 SMTP Submission 由 API 接管

- 新增 `465/587` 提交服务与 TLS 配置，支持 StartTLS 和隐式 TLS。
- 提交时校验认证邮箱、权限和 `From` 一致性，先写入 `Sent` 再转发到后端 SMTP。
- 增加 `Message-ID` 去重与失败回滚，避免重复保存发送副本。
- 调整部署与文档，移除 Postfix 的 submission 监听，改由 LanQin API 对外提供提交端口。

deploy/all-in-one/entrypoint.sh

@@ -7,11 +7,14 @@ set -eu
 : "${LANQIN_ADDR:=127.0.0.1:8080}"
 : "${LANQIN_SMTP_HOST:=127.0.0.1}"
 : "${LANQIN_SMTP_PORT:=25}"
+: "${LANQIN_SUBMISSION_ADDR:=:587}"
+: "${LANQIN_SUBMISSION_TLS_ADDR:=:465}"
+: "${LANQIN_SUBMISSION_MAX_MESSAGE_MB:=35}"
 : "${LANQIN_MAILDIR_ROOT:=/var/mail/vhosts}"
 : "${LANQIN_TLS_CERT_FILE:=}"
 : "${LANQIN_TLS_KEY_FILE:=}"
 
-export LANQIN_DATA_DIR LANQIN_DB_PATH LANQIN_ADDR LANQIN_SMTP_HOST LANQIN_SMTP_PORT LANQIN_MAILDIR_ROOT
+export LANQIN_DATA_DIR LANQIN_DB_PATH LANQIN_ADDR LANQIN_SMTP_HOST LANQIN_SMTP_PORT LANQIN_SUBMISSION_ADDR LANQIN_SUBMISSION_TLS_ADDR LANQIN_SUBMISSION_MAX_MESSAGE_MB LANQIN_MAILDIR_ROOT LANQIN_TLS_CERT_FILE LANQIN_TLS_KEY_FILE
 
 addgroup --system --gid 5000 vmail 2>/dev/null || true
 adduser --system --uid 5000 --gid 5000 --home /var/mail/vhosts --no-create-home vmail 2>/dev/null || true
@@ -47,7 +50,6 @@ postconf -e "myorigin = ${LANQIN_PUBLIC_HOSTNAME}"
 postconf -e "smtpd_tls_cert_file = ${TLS_CERT}"
 postconf -e "smtpd_tls_key_file = ${TLS_KEY}"
 postconf -e "virtual_transport = lmtp:inet:127.0.0.1:24"
-postconf -e "smtpd_sasl_path = inet:127.0.0.1:12345"
 postconf -e "milter_mail_macros = i {mail_addr} {client_addr} {client_name} {auth_authen}"
 postconf -e "smtpd_milters = inet:127.0.0.1:11332"
 postconf -e "non_smtpd_milters = inet:127.0.0.1:11332"