[pfx] Re: SMTPUTF8
Gerald Galster via Postfix-users <[email protected]> Fri, 3 Jul 2026 01:51:07 +0200
| Newsgroups | gmane.mail.postfix.user |
|---|---|
| Message-ID | <[email protected]> |
--===============5304039352657154139== Content-Type: multipart/alternative; boundary="Apple-Mail=_06DF5E89-5CD8-4E76-A3E0-8976AE19AAB8" --Apple-Mail=_06DF5E89-5CD8-4E76-A3E0-8976AE19AAB8 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > 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: >>> -=3D-=3D-=3D-=3D-=3D- >>> -=3D-=3D-=3D-=3D-=3D- >>>=20 >>> Hi. >>>=20 >>> We have strange letters here. (=C3=A6=C3=B8=C3=A5=C3=86=C3=98=C3=85). >>=20 >> 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 vestskovsl=C3=B8bet.dk xn--vestskovslbet-knb.dk $ idn2 -d xn--vestskovslbet-knb.dk vestskovsl=C3=B8bet.dk >>> 3E0D010E0084: to=3D<stefan@vestskovsl=C3=B8bet.dk>,=20 >>> relay=3Dmx.simply.com[94.231.106.20]:25, delay=3D0.88,=20 >>> delays=3D0.46/0.1/0.32/0, dsn=3D5.6.7, status=3Dbounced (SMTPUTF8 is = required,=20 >>> but was not offered by host mx.simply.com[94.231.106.20]) >>=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. >>=20 >> A possible workaround is to send mail to the A-label version of the=20= >> address, [email protected] which would not need = SMTPUTF8. >> I poked at the server and it accepted that address. >=20 >=20 > Is there a reason why this is not attempted automatically? That's the way browsers do it. A URL like http://vestskovsl=C3=B8bet.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 = vestskovsl=C3=B8bet.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/WS5X= U7ULAN6KAXK4JR6GZK26J56ON3GP/ 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 --Apple-Mail=_06DF5E89-5CD8-4E76-A3E0-8976AE19AAB8 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8 <html><head><meta http-equiv=3D"content-type" content=3D"text/html; = charset=3Dutf-8"></head><body style=3D"overflow-wrap: break-word; = -webkit-nbsp-mode: space; line-break: after-white-space;"><br = id=3D"lineBreakAtBeginningOfMessage"><div><br><blockquote = type=3D"cite"><div>Danjel Jungersen via Postfix-users = <[email protected]>:</div><div><span style=3D"caret-color: = rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 11px; font-style: = normal; font-variant-caps: normal; font-weight: 400; letter-spacing: = normal; text-align: start; text-indent: 0px; text-transform: none; = white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none; float: none; display: inline !important;">On 2 = July 2026 22:55:34 CEST, John Levine <</span><a = href=3D"mailto:[email protected]" style=3D"font-family: Menlo-Regular; = font-size: 11px; font-style: normal; font-variant-caps: normal; = font-weight: 400; letter-spacing: normal; orphans: auto; text-align: = start; text-indent: 0px; text-transform: none; white-space: normal; = widows: auto; word-spacing: 0px; -webkit-text-stroke-width: = 0px;">[email protected]</a><span style=3D"caret-color: rgb(0, 0, 0); = font-family: Menlo-Regular; font-size: 11px; font-style: normal; = font-variant-caps: normal; font-weight: 400; letter-spacing: normal; = text-align: start; text-indent: 0px; text-transform: none; white-space: = normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none; float: none; display: inline !important;">> = wrote:</span><br style=3D"caret-color: rgb(0, 0, 0); font-family: = Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: = normal; font-weight: 400; letter-spacing: normal; text-align: start; = text-indent: 0px; text-transform: none; white-space: normal; = word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: = none;"><blockquote type=3D"cite" style=3D"font-family: Menlo-Regular; = font-size: 11px; font-style: normal; font-variant-caps: normal; = font-weight: 400; letter-spacing: normal; orphans: auto; text-align: = start; text-indent: 0px; text-transform: none; white-space: normal; = widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none;">It appears that Danjel Jungersen via = Postfix-users <[email protected]> said:<br><blockquote = type=3D"cite">-=3D-=3D-=3D-=3D-=3D-<br>-=3D-=3D-=3D-=3D-=3D-<br><br>Hi.<br= ><br>We have strange letters here. = (=C3=A6=C3=B8=C3=A5=C3=86=C3=98=C3=85).<br></blockquote><br>That's an = Internationalized Domain Name (IDN), in the Unicode U-label form.<br>THe = encoded A-label equivalent which you can look up in the DNS is = xn--vestskovslbet-knb.dk<br></blockquote></div></blockquote><div><br></div= ><div>A common tool for conversion is = idn2:</div><div><br></div><div><div> $ idn2 = vestskovsl=C3=B8bet.dk</div><div> = xn--vestskovslbet-knb.dk</div><div><br></div><div> $ idn2 -d = xn--vestskovslbet-knb.dk</div><div> = vestskovsl=C3=B8bet.dk</div></div><br><blockquote = type=3D"cite"><div><blockquote type=3D"cite" style=3D"font-family: = Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: = normal; font-weight: 400; letter-spacing: normal; orphans: auto; = text-align: start; text-indent: 0px; text-transform: none; white-space: = normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none;"><blockquote type=3D"cite">3E0D010E0084: = to=3D<stefan@vestskovsl=C3=B8bet.dk>,<span = class=3D"Apple-converted-space"> </span><br>relay=3Dmx.simply.com[94.= 231.106.20]:25, delay=3D0.88,<span = class=3D"Apple-converted-space"> </span><br>delays=3D0.46/0.1/0.32/0,= dsn=3D5.6.7, status=3Dbounced (SMTPUTF8 is required,<span = class=3D"Apple-converted-space"> </span><br>but was not offered by = host mx.simply.com[94.231.106.20])<br></blockquote><br>His = correspondent's mail is misconfigured. If a mail server is going = to<br>handle mail with IDN addresses, it needs to enable the SMTPUTF8 = feature<br>which his provider mx.simply.com has not done. That is = their mistake,<br>they have to fix it.<br><br>A possible workaround is = to send mail to the A-label version of the<span = class=3D"Apple-converted-space"> </span><br>address, = [email protected] which would not need SMTPUTF8.<br>I = poked at the server and it accepted that address.<br></blockquote><br = style=3D"caret-color: rgb(0, 0, 0); font-family: Menlo-Regular; = font-size: 11px; font-style: normal; font-variant-caps: normal; = font-weight: 400; letter-spacing: normal; text-align: start; = text-indent: 0px; text-transform: none; white-space: normal; = word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: = none;"><br style=3D"caret-color: rgb(0, 0, 0); font-family: = Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: = normal; font-weight: 400; letter-spacing: normal; text-align: start; = text-indent: 0px; text-transform: none; white-space: normal; = word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: = none;"><span style=3D"caret-color: rgb(0, 0, 0); font-family: = Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: = normal; font-weight: 400; letter-spacing: normal; text-align: start; = text-indent: 0px; text-transform: none; white-space: normal; = word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: = none; float: none; display: inline !important;">Is there a reason why = this is not attempted automatically?</span><br style=3D"caret-color: = rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 11px; font-style: = normal; font-variant-caps: normal; font-weight: 400; letter-spacing: = normal; text-align: start; text-indent: 0px; text-transform: none; = white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none;"></div></blockquote><div><br></div><div>That's = the way browsers do it. A URL like http://vestskovsl=C3=B8bet.dk/ = will</div><div>internally be converted to xn--vestskovslbet-knb.dk = and sent as the HTTP</div><div>Hostname. The remote webserver usually = has <span style=3D"caret-color: rgb(0, 0, 0); color: rgb(0, 0, = 0);">xn--vestskovslbet-knb.dk</span></div><div><span style=3D"caret-color:= rgb(0, 0, 0); color: rgb(0, 0, 0);">configured as ServerName oder = ServerAlias (Apache), so everything matches.</span></div><div>The URL in = the browser's location bar does not change and shows = vestskovsl=C3=B8bet.dk.</div><div>After all it's just another = representation of the same thing in this = regard.</div><div><br></div><div>Unfortunately MUAs did not support that = mechanism very well. Maybe the situation</div><div>has improved by = now.</div><br><blockquote type=3D"cite"><div><span style=3D"caret-color: = rgb(0, 0, 0); font-family: Menlo-Regular; font-size: 11px; font-style: = normal; font-variant-caps: normal; font-weight: 400; letter-spacing: = normal; text-align: start; text-indent: 0px; text-transform: none; = white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; = text-decoration: none; float: none; display: inline !important;">The = receiver claims that he receives mail from other people using the IDN = version.</span><br style=3D"caret-color: rgb(0, 0, 0); font-family: = Menlo-Regular; font-size: 11px; font-style: normal; font-variant-caps: = normal; font-weight: 400; letter-spacing: normal; text-align: start; = text-indent: 0px; text-transform: none; white-space: normal; = word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: = none;"></div></blockquote><div><br></div><div>Does the receiver's MUA = transparently convert domain names?</div><div><br></div><div>I advise to = thoroughly check mailsystems before enabling SMTPUTF8, = especially</div><div>in combination with backends like dovecot as an = LMTP server.</div><div><br></div><div>At least dovecot 2.4.1 was not = ready for = SMTPUTF8:</div><div>https://dovecot.org/mailman3/archives/list/dovecot@dov= ecot.org/thread/WS5XU7ULAN6KAXK4JR6GZK26J56ON3GP/</div><div><br></div><div= >And think of arbitrary mailsystems that might have enabled SMTPUTF8 = without</div><div>having verified backend compatibility and what that = means for reliable delivery.</div><div><br></div><div>Best = regards,</div><div>Gerald</div><div><br></div><div><br></div><div><br></di= v></div></body></html>= --Apple-Mail=_06DF5E89-5CD8-4E76-A3E0-8976AE19AAB8-- --===============5304039352657154139== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Postfix-users mailing list -- [email protected] To unsubscribe send an email to [email protected] --===============5304039352657154139==--