I'm setting up a mailserver solution (Postfix, Dovecot) and I'm wondering about IDN (Internationalized domain name) on the IMAP / POP3 side.

Should I use the ASCII-encoded (PUNY / ACE) format for Dovecot user logins or should users rather login with the "user-friendy" Unicode format?

I'm almost sure the ASCII-encoded domain name is the right answer here, but i realy didn't found any clear answer on that matter anywhere on the internet..

Am I right about this?

Thank you.

  • 1
    You have to look at every client software documentation and if they support Unicode-format. I would guess about 90% of software do not support Unicode-format and you have to use PUNY / ACE -format. Apr 23, 2015 at 22:25
  • I would expect something about this matter in IMAP / POP3 RFC standard, but i found nothing. Is the format realy unspecified here? It feels strange..
    – dave
    Apr 23, 2015 at 22:36

1 Answer 1


The right answer is to use the ACE format (xn--XXXXX.tld).

In theory, Dovecot does not have a problem working with more or less any characters in domain name (but it has to be enabled in its configuration via auth_username_chars).

On the other hand, MUAs doesn't seem to support this, they expect the ascii-encoded string (though i thing they could support that or at least accept the unicode string and convert it to ACE internaly for better user experience).

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