> Danjel Jungersen via Postfix-users <[email protected]>: > On 2 July 2026 22:55:34 CEST, John Levine <[email protected] > <mailto:[email protected]>> wrote: >> It appears that Danjel Jungersen via Postfix-users <[email protected]> >> said: >>> -=-=-=-=-=- >>> -=-=-=-=-=- >>> >>> Hi. >>> >>> We have strange letters here. (æøåÆØÅ). >> >> That's an Internationalized Domain Name (IDN), in the Unicode U-label form. >> THe encoded A-label equivalent which you can look up in the DNS is >> xn--vestskovslbet-knb.dk
A common tool for conversion is idn2: $ idn2 vestskovsløbet.dk xn--vestskovslbet-knb.dk $ idn2 -d xn--vestskovslbet-knb.dk vestskovsløbet.dk >>> 3E0D010E0084: to=<stefan@vestskovsløbet.dk>, >>> relay=mx.simply.com[94.231.106.20]:25, delay=0.88, >>> delays=0.46/0.1/0.32/0, dsn=5.6.7, status=bounced (SMTPUTF8 is required, >>> but was not offered by host mx.simply.com[94.231.106.20]) >> >> His correspondent's mail is misconfigured. If a mail server is going to >> handle mail with IDN addresses, it needs to enable the SMTPUTF8 feature >> which his provider mx.simply.com has not done. That is their mistake, >> they have to fix it. >> >> A possible workaround is to send mail to the A-label version of the >> address, [email protected] which would not need SMTPUTF8. >> I poked at the server and it accepted that address. > > > Is there a reason why this is not attempted automatically? That's the way browsers do it. A URL like http://vestskovsløbet.dk/ will internally be converted to xn--vestskovslbet-knb.dk and sent as the HTTP Hostname. The remote webserver usually has xn--vestskovslbet-knb.dk configured as ServerName oder ServerAlias (Apache), so everything matches. The URL in the browser's location bar does not change and shows vestskovsløbet.dk. After all it's just another representation of the same thing in this regard. Unfortunately MUAs did not support that mechanism very well. Maybe the situation has improved by now. > The receiver claims that he receives mail from other people using the IDN > version. Does the receiver's MUA transparently convert domain names? I advise to thoroughly check mailsystems before enabling SMTPUTF8, especially in combination with backends like dovecot as an LMTP server. At least dovecot 2.4.1 was not ready for SMTPUTF8: https://dovecot.org/mailman3/archives/list/[email protected]/thread/WS5XU7ULAN6KAXK4JR6GZK26J56ON3GP/ And think of arbitrary mailsystems that might have enabled SMTPUTF8 without having verified backend compatibility and what that means for reliable delivery. Best regards, Gerald
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