feat(email): 初始化自建邮箱 MVP

- 新增 Go + SQLite 后端，支持登录、域名、邮箱、别名、联系人、规则、统计与邮件收发。
- 新增 Webmail 前端，支持多邮箱切换、邮件列表/阅读/写信、附件、搜索、主题切换与个人中心。
- 新增 Docker Compose 部署骨架，补充 Postfix、Dovecot、OpenDKIM、Nginx 配置与部署说明。

deploy/postfix/Dockerfile

@@ -0,0 +1,10 @@
+FROM debian:bookworm-slim
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && apt-get install -y --no-install-recommends postfix postfix-sqlite ca-certificates rsyslog && rm -rf /var/lib/apt/lists/*
+COPY main.cf /etc/postfix/main.cf
+COPY master.cf /etc/postfix/master.cf
+COPY sqlite-*.cf /etc/postfix/
+COPY entrypoint.sh /entrypoint.sh
+RUN chmod +x /entrypoint.sh
+EXPOSE 25 587
+CMD ["/entrypoint.sh"]

deploy/postfix/entrypoint.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+set -eu
+: "${LANQIN_PUBLIC_HOSTNAME:=mail.example.com}"
+postconf -e "myhostname = ${LANQIN_PUBLIC_HOSTNAME}"
+postconf -e "myorigin = ${LANQIN_PUBLIC_HOSTNAME}"
+postconf -e "smtpd_milters = inet:opendkim:8891"
+postconf -e "non_smtpd_milters = inet:opendkim:8891"
+postfix check
+exec postfix start-fg

deploy/postfix/main.cf

@@ -0,0 +1,30 @@
+compatibility_level = 3.6
+myhostname = mail.example.com
+myorigin = $myhostname
+mydestination = localhost
+inet_interfaces = all
+inet_protocols = all
+
+# SQLite maps read the same LanQin DB created by the Go API.
+virtual_mailbox_domains = sqlite:/etc/postfix/sqlite-domains.cf
+virtual_mailbox_maps = sqlite:/etc/postfix/sqlite-mailboxes.cf
+virtual_alias_maps = sqlite:/etc/postfix/sqlite-aliases.cf
+virtual_transport = lmtp:inet:dovecot:24
+virtual_mailbox_base = /var/mail/vhosts
+
+smtpd_banner = $myhostname ESMTP LanQin Email
+smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
+smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
+
+# Submission auth via Dovecot.
+smtpd_sasl_type = dovecot
+smtpd_sasl_path = inet:dovecot:12345
+smtpd_sasl_auth_enable = yes
+smtpd_tls_security_level = may
+smtp_tls_security_level = may
+
+# DKIM milter.
+milter_protocol = 6
+milter_default_action = accept
+smtpd_milters = inet:opendkim:8891
+non_smtpd_milters = inet:opendkim:8891

deploy/postfix/master.cf

@@ -0,0 +1,29 @@
+smtp      inet  n       -       y       -       -       smtpd
+submission inet n       -       y       -       -       smtpd
+  -o syslog_name=postfix/submission
+  -o smtpd_tls_security_level=may
+  -o smtpd_sasl_auth_enable=yes
+  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
+pickup    unix  n       -       y       60      1       pickup
+cleanup   unix  n       -       y       -       0       cleanup
+qmgr      unix  n       -       n       300     1       qmgr
+tlsmgr    unix  -       -       y       1000?   1       tlsmgr
+rewrite   unix  -       -       y       -       -       trivial-rewrite
+bounce    unix  -       -       y       -       0       bounce
+defer     unix  -       -       y       -       0       bounce
+trace     unix  -       -       y       -       0       bounce
+verify    unix  -       -       y       -       1       verify
+flush     unix  n       -       y       1000?   0       flush
+proxymap  unix  -       -       n       -       -       proxymap
+proxywrite unix -       -       n       -       1       proxymap
+smtp      unix  -       -       y       -       -       smtp
+relay     unix  -       -       y       -       -       smtp
+showq     unix  n       -       y       -       -       showq
+error     unix  -       -       y       -       -       error
+retry     unix  -       -       y       -       -       error
+discard   unix  -       -       y       -       -       discard
+local     unix  -       n       n       -       -       local
+virtual   unix  -       n       n       -       -       virtual
+lmtp      unix  -       -       y       -       -       lmtp
+anvil     unix  -       -       y       -       1       anvil
+scache    unix  -       -       y       -       1       scache

deploy/postfix/sqlite-aliases.cf

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+dbpath = /data/lanqin.db
+query = SELECT destination FROM aliases WHERE source='%s' AND enabled=1 UNION SELECT address FROM mailboxes WHERE address='%s' AND status='active'

deploy/postfix/sqlite-domains.cf

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+dbpath = /data/lanqin.db
+query = SELECT 1 FROM domains WHERE name='%s' AND status='active'

deploy/postfix/sqlite-mailboxes.cf

@@ -0,0 +1,2 @@
+dbpath = /data/lanqin.db
+query = SELECT 'vhosts/' || substr(address, instr(address, '@') + 1) || '/' || local_part || '/Maildir/' FROM mailboxes WHERE address='%s' AND status='active'