SMTPUTF8 is required, but was not offered by host

[DEZERTIR]

Good day, my name is Vladimir. I encountered a problem, the sender cannot deliver the letter to me. I found this problem in the PMG logs, please tell me how to solve it:
My PMG version: 8.2.0

2025-08-25T06:58:39.819950+03:00 pmg2 postfix/smtpd[2415515]: connect from send82.i.mail.ru[89.221.237.177]
2025-08-25T06:58:39.913350+03:00 pmg2 postfix/smtpd[2415515]: Anonymous TLS connection established from send82.i.mail.ru[89.221.237.177]: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256
2025-08-25T06:58:40.032979+03:00 pmg2 postfix/smtpd[2415515]: 080571C0F58: client=send82.i.mail.ru[89.221.237.177]
2025-08-25T06:58:40.035505+03:00 pmg2 postfix/cleanup[2415196]: 080571C0F58: message-id=<E1uqOLo-00000000I7h-24Sj.robot_imd-mail-ru@exim-smtp-889c6486-flkl5>
2025-08-25T06:58:40.086824+03:00 pmg2 postfix/qmgr[33961]: 080571C0F58: from=<robot_imd@mail.ru>, size=157034, nrcpt=2 (queue active)
2025-08-25T06:58:40.086947+03:00 pmg2 postfix/smtpd[2415515]: disconnect from send82.i.mail.ru[89.221.237.177] ehlo=2 starttls=1 mail=1 rcpt=2 bdat=2 quit=1 commands=9
2025-08-25T06:58:40.139750+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: new mail message-id=<E1uqOLo-00000000I7h-24Sj.robot_imd-mail-ru@exim-smtp-889c6486-flkl5>#012
2025-08-25T06:58:40.401709+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: found archive '%41E%441%442%430%442%43A%438 %43D%430 %441%43A%43B-1.xls' (application/zip)
2025-08-25T06:58:40.433769+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: unpack archive '%41E%441%442%430%442%43A%438 %43D%430 %441%43A%43B-1.xls' done (31 ms)
2025-08-25T06:58:45.640547+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: SA score=0/5 time=5.164 bayes=0.00 autolearn=ham autolearn_force=no =AWL(0.226),BAYES_00(-1.9),DKIM_SIGNED(0.1),DKIM_VALID(-0 hits),DKIM_VALID_AU(-0.1),DKIM_VALID_EF(-0.1),DMARC_PAS S(-0.1),FREEMAIL_FROM(0.001),RU_WENTOR_RCPTS_3(0.01),SPF_HELO_PASS(-0.001),SPF_PASS(-0.001),TVD_SPACE_RATIO(0.001)
2025-08-25T06:58:45.642499+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: added disclaimer (rule: External Warning)
2025-08-25T06:58:45.642717+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: added disclaimer (rule: External Warning)
2025-08-25T06:58:45.643808+03:00 pmg2 postfix/smtpd[2415202]: connect from localhost.localdomain[127.0.0.1]
2025-08-25T06:58:45.645140+03:00 pmg2 postfix/smtpd[2415202]: 9D7911C0F5C: client=localhost.localdomain[127.0.0.1], orig_client=send82.i.mail.ru[89.221.237.177]
2025-08-25T06:58:45.646418+03:00 pmg2 postfix/cleanup[2415279]: 9D7911C0F5C: message-id=<E1uqOLo-00000000I7h-24Sj.robot_imd-mail-ru@exim-smtp-889c6486-flkl5>
2025-08-25T06:58:45.707352+03:00 pmg2 postfix/qmgr[33961]: 9D7911C0F5C: from=<robot_imd@mail.ru>, size=157987, nrcpt=2 (queue active)
2025-08-25T06:58:45.707446+03:00 pmg2 postfix/smtpd[2415202]: disconnect from localhost.localdomain[127.0.0.1] ehlo=1 xforward=1 mail=1 rcpt=2 data=1 commands=6
2025-08-25T06:58:45.707554+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: accept mail to <logistskz@dkc.ru> (9D7911C0F5C) (rule: Whitelist)
2025-08-25T06:58:45.707605+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: accept mail to <mikhail.shapenkov@dkc.ru> (9D7911C0F5C) (rule: Whitelist)
2025-08-25T06:58:45.711134+03:00 pmg2 pmg-smtp-filter[2414743]: 1C0F5B68ABDF701F8C9: processing time: 5.577 seconds (5.164, 0.26, 0)
2025-08-25T06:58:45.711451+03:00 pmg2 postfix/lmtp[2415197]: 080571C0F58: to=<logistskz@dkc.ru>, relay=127.0.0.1[127.0.0.1]:10024, delay=5.7, delays=0.11/0/0.04/5.6, dsn=2.5.0, status=sent (250 2.5.0 OK (1C0F5B68ABDF701F8C9))
2025-08-25T06:58:45.719893+03:00 pmg2 postfix/smtp[2415203]: 9D7911C0F5C: to=<logistskz@dkc.ru>, relay=mail.dkc.ru[192.168.50.10]:25, delay=0.07, delays=0.06/0/0/0, dsn=5.6.7, status=bounced (SMTPUTF8 is required, but was not offered by host mail.dkc.ru[192.168.50.10])
2025-08-25T06:58:45.722228+03:00 pmg2 postfix/smtp[2415203]: 9D7911C0F5C: to=<mikhail.shapenkov@dkc.ru>, relay=mail.dkc.ru[192.168.50.10]:25, delay=0.07, delays=0.06/0/0/0, dsn=5.6.7, status=bounced (SMTPUTF8 is required, but was not offered by host mail.dkc.ru[192.168.50.10])
2025-08-25T06:58:45.726748+03:00 pmg2 postfix/qmgr[33961]: 9D7911C0F5C: removed
2025-08-25T06:58:45.751737+03:00 pmg2 postfix/lmtp[2415197]: 080571C0F58: to=<mikhail.shapenkov@dkc.ru>, relay=127.0.0.1[127.0.0.1]:10024, delay=5.8, delays=0.11/0/0.04/5.6, dsn=2.5.0, status=sent (250 2.5.0 OK (1C0F5B68ABDF701F8C9))

 

[mmisolution]

Hello,

we have had the issue also.

If 'smtputf8_enable = yes' is used, then any header with non-ascii, or in MAIL FROM or RCPT TO must be in utf-8.
That is, the other side must support SMTPUTF8 option too.

Older Exchangeservers < 2019 does not have that option, and connection with them fails.

Working solution :
edit /etc/pmg/pmg.conf
and in the "mail" section put smtputf8 at value 0

A better solution that forcing always or using none, would be to propose SMTPUTF8,
and still accept a raw bit connection if the other side send 8bit data without SMTPUTF8
(but that is a functionality/behaviour of the underlying postfix)

We were impacted by that when we added a new customer that still had a 2021 Exchange.

 

[DEZERTIR]

Hello,

we have had the issue also.

If 'smtputf8_enable = yes' is used, then any header with non-ascii, or in MAIL FROM or RCPT TO must be in utf-8.
That is, the other side must support SMTPUTF8 option too.

Older Exchangeservers < 2019 does not have that option, and connection with them fails.

Working solution :
edit /etc/pmg/pmg.conf
and in the "mail" section put smtputf8 at value 0

A better solution that forcing always or using none, would be to propose SMTPUTF8,
and still accept a raw bit connection if the other side send 8bit data without SMTPUTF8
(but that is a functionality/behaviour of the underlying postfix)

We were impacted by that when we added a new customer that still had a 2021 Exchange.

Thanks for the tip
Can you please clarify from my log whether this error is related to a problem on the sender's side, or is the problem on my side when transmitting via PMG to the mail server?