Hello, The definition "Punycode is an algorithm that converts an IDN into an ASCII string that starts with xn--. The Punycode algorithm is bi-directional. " needs some adjustment. xn--abcdeddaa where "xn--" is a prefix and "abcdeddaa" is output of the Punycode algorithm. So Punycode output does not include "xn--". ======================================following are texts from RFC5890=============================== " the string following "xn--" must be the valid output of the Punycode algorithm and must be convertible into valid U-label form." "An "A-label" is the ASCII-Compatible Encoding (ACE, see Section 2.3.2.5) form of an IDNA-valid string. It must be a complete label: IDNA is defined for labels, not for parts of them and not for complete domain names. This means, by definition, that every A-label will begin with the IDNA ACE prefix, "xn--" (see Section 2.3.2.5), followed by a string that is a valid output of the Punycode algorithm [RFC3492] and hence a maximum of 59 ASCII characters in length. " Jiankang Yao From: Don Hollander Date: 2017-01-22 17:33 To: ua-eai@icann.org CC: Tan Tanaka, Dennis; Mark Svancarek via UA-Coordination; Dr. AJAY D A T A; Stuart Stuple Subject: [UA-Coordination] Revised UASG013 - Quick Guide to EAI Last month I sent out a formatted Quick Guide to EAI. This resulted in a number of comments from Ajay, Stuart, Mark, Lars & Dennis. These enhancements were mostly focused on the Email Service Provider. I have revised the source document which is attached. And for reference, I’m also including the formatted earlier draft. Could I please get any final comments by the end of this week (25th)? Thanks. Don Don Hollander Universal Acceptance Steering Group Skype: don_hollander

Hi UA-EAI team, Few comments and questions regarding the quick guide for discussion: (1) Client Software (MUA – Mail User Agent) - Should pass the domain name to the MTA (Mail Transport Agent) in A-Label format (RFC5890) The idea of EAI is to allow native Unicode in UTF8 in all mail exchange, is there any rationale for this recommendation? This also makes mailbox management more unnecessary complicated when the next recommendation is 'Should store and display the Mailbox in Unicode'. (2) Consider offering mailbox names which conform to the domain name label generation rules for the selected script. - Such names are guaranteed to be compatible with the Punycode algorithm. Punycode is one of many encoding solution, and it (assuming we are talking about punycode under IDNA2008) has drawback. This limits the characters allowed in mailbox name. While some may found it okay, it should be pointed out. (3) Consider offering mailbox names which conform to the domain name label generation rules for the selected script. - These email addresses can easily be shared by users with their friends and colleagues who do not use their same writing method; the colleague or friend can address email to such an address, or create an address book entry, using the A-label format. Since there's a recommendation earlier to offer an all-ASCII email address, I think this recommendation is not necessary. If one isn't using the same writing method (or the same language/character), it might be better storing the all-ASCII name than than the 'A-label' name. It's easier to manage 'josephyee' than 'xn--qoqx77cy1a' which rely on mail client or backend to render it back properly. (4) Upon use, the client MUA software should convert the A-Label to the appropriate U-Label, at which point the friend or colleague will possess the EAI formatted email address despite not having a keyboard or IME which supports the target script. First, this one is more of a recommendation for mail client section than mail service provider section. Second, please see below for a more in depth discussion on the whole encoding mailbox name. (5) How to ensure delivery to non-EAI ready mail systems - Normalising mailbox names in non-ASCII scripts If the recipient is non-EAI ready mail systems, normalising mailbox names would not help. Non-ASCII characters still exist in the mailbox name after normalization. ***** (Note: I'm co-chair of EAI working group at IETF, but I speak as individual only) On Encoding (A-label, punycode, etc) mailbox name At EAI working group, the notion of encoding the UTF8 mailbox name into pure-ASCII mailbox had been discussed, and there is no recommendation made on it. Mailbox management is different from domain management, applying the same encoding algorithm may sound intuitive as domain name already used it and seeming of consistent because the same encoding was provided on both sides of the @ sign. The first drawback, as mentioned above, is the limitation of characters allowed in local part. There are legit ASCII characters/symbols (!#$_) for email that won't make it with A-label. The second drawback is that some characters being used in human name may be prohibited under IDNA2008. There are another category of concerns with pure punycode algorithm on mailbox name. Also, there are not enough coverage on ensuring various presentations of mail address to map to the same mailbox. I have serious concern on recommending this practice. This practice is neither mandatory standard nor best common practice, it probably would not be consistently implemented across mail clients, and I would not be surprise if some implementer were against this. While we can recommend to think-about/adopt encoding practice, I'm concern that we need to expand more writing to the quick guide. If there's a strong desire to push for an encoding practice, there's a need for another in depth writing on pros & cons, deployment and operation needs, what works & what doesn't. Best, Joseph On Sun, Jan 22, 2017 at 4:33 AM, Don Hollander <don.hollander@icann.org> wrote:

Last month I sent out a formatted Quick Guide to EAI.

This resulted in a number of comments from Ajay, Stuart, Mark, Lars & Dennis.

These enhancements were mostly focused on the Email Service Provider.

I have revised the source document which is attached.

And for reference, I’m also including the formatted earlier draft.

Could I please get any final comments by the end of this week (25th)?

Thanks.

Don

Don Hollander Universal Acceptance Steering Group Skype: don_hollander

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