On Sun, Oct 18, 2026 at 03:09:36PM +0200, Danjel Jungersen via Postfix-users 
wrote:
The remote user did reply, but the incoming mail was not delivered.

2026-10-12T18:40:50.760730+02:00 mail postfix/lmtp[116517]:
  EFCA110E01DB: to=<[email protected]>,
  relay=mail.jungersen.dk[private/dovecot-lmtp], delay=1.8,
  delays=1.7/0.07/0.09/0, dsn=5.6.7, status=bounced
  (SMTPUTF8 is required, but was not offered by host 
mail.jungersen.dk[private/dovecot-lmtp])

As I read this, the remote serve requires utf8, but also uses the
alternative utf8-free address.

On 19.10.26 00:34, Viktor Dukhovni via Postfix-users wrote:
Not the remote server, rather your Dovecot LMTP service listening on a
unix-domain socket.  You need to enable SMTPUTF8 support in the dovecot
LMTP service.

My friendly AI suggests:

 Historical Context vs. Modern Support

   Historically (Dovecot v2.3 and earlier):
     Dovecot did not support SMTPUTF8 in its LMTP implementation.
     Administrators integrating Postfix with Dovecot LMTP were
     routinely advised to set smtputf8_enable = no in Postfix to
     prevent delivery failures when emails contained non-ASCII
     characters or emojis.

Wasn't there issue with DKIM signatures and utf-8?
IIRC, when decoding from utf-8 the DKIM signature was invalidated. That means, when delivering message with utf-8 headers and DKIM signature to utf-8 incapable mail server, recoding it would break the signature.

The proposed workaround was disabling smtputf8 thus asking the sender to decode such mail before dkim-signing.

On 18.10.26 16:08, Danjel Jungersen via Postfix-users wrote:
Running debian bookworm, which have dovecot 2.3.19.

Thank you for pointing this out, I will look into options for upgrading.

I have read that there are a couple of issues that make it hard to do an upgrade, a migration is needed (or at least advised).

I believe it was dovecot that changed the way of working.

Dovecot 2.4 introduces new config format, so you must convert/change your files.
This is reason why I haven't done so yet (besides being overloaded with work). The conversion should be easy and there is apparently script to do that for you.
I haven't tried it yet...

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