Postfix 自從 Debian Linux 升級到 Buster 後，內部信就寄不出去也收不到了，來研究看看怎麼解決~
Postfix 修正 fatal: in parameter smtpd_relay_restrictions 等問題
- $ tail -f /var/log/mail.info # 出現下述錯誤：
- postfix[22076]: Postfix is running with backwards-compatible default settings
- postfix[22076]: See http://www.postfix.org/COMPATIBILITY_README.html for details
- postfix[22076]: To disable backwards compatibility use "postconf compatibility_level=2" and "postfix reload"
- 主要是下面這行：
- postfix/smtpd[5251]: fatal: in parameter smtpd_relay_restrictions or smtpd_recipient_restrictions, specify at least one working instance of: reject_unauth_destination, defer_unauth_destination, reject, defer, defer_if_permit or check_relay_domains
看起來解法有兩種：
- 設定降低相容性，/etc/postfix/main.cf 加入下述：(我沒用這招，不確定是否可行)
- compatibility_level=2 # 可查看這個 postconf -e compatibility_level=2 # 可測試
- 設定檔 /etc/postfix/main.cf 加入下述：(我用這個，直接加在最後一行即可)
- smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination
- $ sudo systemctl restart postfix # 即可收到信囉~
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- smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated reject_unauth_destination