Arnt Gulbrandsen
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2017-01-07

Use UTF8 or Punycode for email addresses?

Unicode addresses in email, such as مثال@مثال.السعودية, can be written using either Punycode or UTF8. (Or, if you're feeling inventive, in another manner you invent.) Which is best?

UTF8 looks like this: From: Arabic Example <مثال@مثال.السعودية>, punycode is From: Arabic Example <xn--mgbh0fb@xn--mgbh0fb.xn--mgberp4a5d4ar>.

The answer follows from two of the design goals for the unicode email extensions:

  1. Allow UTF8 everywhere
  2. Extend email, don't restrict it

RFC 821 and its successors do not contain any rules such as you MUST NOT put the letter n next to an x, so Punycode is allowed. EAI allows Punycode by virtue of not forbidding what was previously allowed. But the right way is to use UTF8 everywhere. Use UTF8 in the subject field, in the body text, in the address… everywhere! That's allowed, it's a design goal, and it's better than Punycode for four reasons.

First, it's simpler than using Punycode in addresses, 2047 encoding in the subject text and qp/b64 encoding in the body text.

Second, it's very, very readable. A surprising amount of legacy software does the right thing if you send it UTF8, and that goes for humans who read email source too.

Third, Punycode's interpretation is only specified for domains, and if rumour is to be believed, people are using two incompatible encodings for the localpart. (In the example above, the second and third instances of xn-- are specified, but the first is not and one vendor reputedly does it differently.) You're permitted to send a punycoded localpart to anyone, but the recipient is not required to interpret it in the way you intend.

Fourth, sending Punycode habituates users to accept random hex blobs in addresses. A phisher's dream.

So use UTF8 everywhere in the message. Mapping to Punycode is necessary when doing the MX lookup in order to transmit the message, but only then.

2016-12-02

A list of free email providers

I've updated my list of free email providers and put it on github, removing many domains that no longer offer such services. freemail.txt contains a one-per-line list of domains that offer free email. There are also scripts to create the list.

2015-02-27

Threading email using Thread-Index

Microsoft Exchange sends email containing a header field called Thread-Index that does much the same job as References. I've no idea why Exchange does that instead of the normal way. But I have found out how to parse it, and it's not terribly difficult. It's easiest to explain using examples, (more…)

2015-02-25

Lack of PGP support in aox

I'm not eager to add any PGP support in Archiveopteryx. That shouldn't be needed, but is, because PGP's signature checking is much stricter than e.g. DKIM's. DKIM thinks a duck is a duck, PGP cares deeply about the details. A quoted-printable duck is not the same as a plaintext duck, and two quoted-printable ducks may not be the same either. Archiveopteryx faithfully implements sixty email-related RFCs and mail stored in or processed by aox frequently cannot be verified by PGP.

However. I care about encryption and privacy, and PGP has the mindshare and is widely considered The Solution. The problem with The Solution is that over the years, it has remained steadily at 0.0% adoption. At the moment slightly below 0.005% of email users have PGP keys, and some fraction of those 0.005% actually use PGP. I infer from that number that PGP has defects that block its adoption almost completely. I have some ideas what those defects are, but that doesn't matter, because whatever they are, their result is to block adoption.

This has been the case for 20 years, and by now I consider PGP to be hopeless. PGP hinders encryption and hurts our privacy, it doesn't help. I don't want to write any code to support that. Perhaps only ten lines of code and a few tests are needed, but I just don't want to write even that.

(Am I doing something else? Yes, I am, actually. I'll write about what later.)

Update: After writing the above, I suddenly remembered this old dystopian novel. The scenes in the 31st floor offices remind me of PGP. Worthwhile ernest people working hard, doing the best work they can.

2014-06-12

Implementation notes about unicode mail

I've implemented unicode mail three times now; in Postfix (paid for by CNNIC and not yet integrated), in aox and lastly in an old mail reader I'm porting from the Zaurus PDA to Android (unreleased as yet, send me mail if you'd like beta access). This is mostly a random collection of notes and remarks I collected while writing the code.

The specification was produced by an IETF working group called EAI (short for email address internationalisation). The WG produced two generations of RFCs. First, an experimental series which I ignore, then a revised, simplified and improved series. This covers the second generation, which takes the general position that unicode mail is only sent to recipients who understand it. There is no conversion during transport, and (almost) no fallback to ASCII.

RFC 6530 is an overview/introduction. It points to the other documents, and has some extra text. Worth reading.

6531 describes how unicode addresses are used with SMTP: MAIL FROM, RCPT TO and VRFY accept UTF8 addresses, and there's a safeguard to provoke a syntax error in case a unicode message body would otherwise reach someone who cannot accept it. (more…)

2014-05-09

A unicode email autoresponder

I've set up a test address for the SMTPUTF8 extension created by the IETF EAI working group.

If you send mail to jøran@blåbærsyltetøy.gulbrandsen.priv.no Jøran will send you a stock reply, which you can use to test that unicode mail works in both directions.

For the moment you must be able to send via IPv6. Jøran can send the reply back via either IPv4 or IPv6, but you have to send the initial message via IPv6. I intend to add a v4-capable secondary MX later.

I have or can arrange other testing too; send me mail if you're interested.

2013-07-28

Test messages for unicode mail addresses (EAI)

EAI is a set of RFCs to enable unicode email addresses. jøran@example.com and even jøran@blåbærsyltetøy.no are syntactically valid email addresses. There are RFCs to extend the email message syntax, to transmit these messages via SMTP, access them via POP and IMAP, and to provide read access by unextended IMAP/POP clients.

I wrote a set of test messages for EAI this morning and put them on github. Feel free to send me extensions and corrections.

2012-09-06

Email address internationalisation

EAI defines a set of RFCs to provide non-ASCII email addresses. pål@eksempel.no. I looked at them with a view to implementing that in Archiveopteryx.

The good news: It's simple and sane.

The bad news: I can tell it's possible to spend a lot of time arguing about minor side issues.