SMTPUTF8 is required, but was not offered by host

查看 Email log 記錄檔，會發現因為 SMTPUTF8 is required, but was not offered by host 導致 Email 無法正常寄信：

sudo vim /etc/log/maillog

448 Aug 25 16:38:02 fortop postfix/qmgr[26422]: 92A8AC0A374D: removed
449 Aug 25 16:38:02 fortop postfix/smtp[27679]: A0C63C0A374C: to=jacky.wang@fortop.com.tw, orig_to=root@fortop.fortop.com.tw, relay=fortop.com.tw[220.130.84.72]:25, delay=0.07, delays=0.03/0/0.04/0, dsn=5.6.7, status=bounced (SMTPUTF8 is required, but was not offered by host fortop.com.tw[220.130.84.72])
450 Aug 25 16:38:02 fortop postfix/qmgr[26422]: A0C63C0A374C: removed
451 Aug 25 16:39:46 fortop postfix/postfix-script[28255]: stopping the Postfix mail system
452 Aug 25 16:39:46 fortop postfix/master[26420]: terminating on signal 15
453 Aug 25 16:39:47 fortop postfix/postfix-script[28346]: starting the Postfix mail system
454 Aug 25 16:39:47 fortop postfix/master[28348]: daemon started -- version 3.5.8, configuration /etc/postfix
455 Aug 25 16:40:51 fortop postfix/postfix-script[28822]: stopping the Postfix mail system
456 Aug 25 16:40:51 fortop postfix/master[28348]: terminating on signal 15
457 Aug 25 16:40:51 fortop postfix/postfix-script[28904]: starting the Postfix mail system
458 Aug 25 16:40:52 fortop postfix/master[28906]: daemon started -- version 3.5.8, configuration /etc/postfix
459 Aug 25 16:42:02 fortop postfix/pickup[28907]: 87AE7C0A374C: uid=0 from=
460 Aug 25 16:42:02 fortop postfix/cleanup[29326]: 87AE7C0A374C: message-id=20210825084202.87AE7C0A374C@fortop.fortop.com.tw
461 Aug 25 16:42:02 fortop postfix/qmgr[28908]: 87AE7C0A374C: from=root@fortop.fortop.com.tw, size=2932, nrcpt=2 (queue active)
462 Aug 25 16:42:03 fortop postfix/smtp[29330]: 87AE7C0A374C: to=jacky.wang@fortop.com.tw, relay=fortop.com.tw[220.130.84.72]:25, delay=1.3, delays=0.16/0.05/0.04/1.1, dsn=2.0.0, status=sent (250 mail received, ready to proceed.)
463 Aug 25 16:42:03 fortop postfix/smtp[29330]: 87AE7C0A374C: to=yams0409@fortop.com.tw, relay=fortop.com.tw[220.130.84.72]:25, delay=1.3, delays=0.16/0.05/0.04/1.1, dsn=2.0.0, status=sent (250 mail received, re ady to proceed.)
464 Aug 25 16:42:03 fortop postfix/qmgr[28908]: 87AE7C0A374C: removed
"/var/log/maillog" 464L, 64336C

解決方式

如下設定後重啟 Postfix，即可正常寄信了：

sudo vim /etc/postfix/mail.cf

smtputf8_autodetect_classes = sendmail, verify
smtputf8_enable = no
strict_smtputf8 = no

重啟 Postfix

sudo systemctl restart postfix.service

參考

• Forwarded to devs - Frequent email rejections with "SMTPUTF8 is required, but was not offered by host " | Plesk Forum