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I have frequently thought that one of reasons for the complexity of many standards/guidelines is that they encompass the whole of Unicode and hence there are few constraints and those constraints can be difficult to understand and agree upon.
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<div class="">I posit that with mailbox names, they can be categorised such that each category is more constrained and the constraints are more easily understood.</div>
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<div class="">A mail service provider could impose further constraints.</div>
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<div class="">Categories could be based on writing system/orthography. So one could define Japanese, Korean, Thai ...etc... categories for mailbox names.</div>
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<div class="">Letʼs take category Japanese: A generalised standard could, for example, include some "Common" characters as well as Han, Hiragana and Katakana <a href="http://unicode.org/Public/UCD/latest/ucd/Scripts.txt" class="">unicode.org/Public/UCD/latest/ucd/Scripts.txt</a>.
A mail service provider could, for example, impose a further restriction by not allowing "Common" characters.</div>
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<div class="">I give an example of Korean mailbox names at <a href="http://jsfiddle.net/coas/2uLhcfef" class="">jsfiddle.net/coas/2uLhcfef</a> I only allow a Korean Hangul mailbox names with the provided Korean Hangul domain names.</div>
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<div class="">...and... much more controversially one could define a Symbols category for mailbox names. Determining which symbols could/should be included in such a category would require a lot of research and consideration.</div>
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<div class="">If I was a mail service provider I, most likely, would not allow mixing of categories in mailbox names.</div>
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<div class="">André Schappo</div>
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<blockquote type="cite" class="">
<div class="">On 13 Apr 2019, at 11:28, John Levine <<a href="mailto:john.levine@standcore.com" class="">john.levine@standcore.com</a>> wrote:</div>
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<div class="">In article <<a href="mailto:BYAPR21MB13171918C3D2AC0E8D177983D12F0@BYAPR21MB1317.namprd21.prod.outlook.com" class="">BYAPR21MB13171918C3D2AC0E8D177983D12F0@BYAPR21MB1317.namprd21.prod.outlook.com</a>> you write:<br class="">
<blockquote type="cite" class="">-=-=-=-=-=-<br class="">
UASG has not endorsed emojis as part of mailbox names and I doubt that we ever would. But as mentioned below, some mail systems will take a more liberal approach.<br class="">
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First, I have to say that I am dismayed to see that many in the UASG<br class="">
do not know that mailboxes and domain names are different and always<br class="">
have been. This is an important difference, and it's discussed at<br class="">
some length in UASG 012. This would probably be a good time for<br class="">
everyone who hasn't read that document to read it now, so at least we<br class="">
agree on the underlying facts.<br class="">
<br class="">
As several people have pointed out, there are practically no rules for<br class="">
what characters are technically legal in mailbox names, but that doesn't<br class="">
mean that in practice you can put any junk in an address and expect it <br class="">
to work. For example, this is a valid address:<br class="">
<br class="">
"); @,?~]"@m.jl.ly<br class="">
<br class="">
but that doesn't mean I would hand it out as an address to anyone from<br class="">
whom I wanted mail.<br class="">
<br class="">
Similarly, you can technically put random combinations of Hindi,<br class="">
Arabic, Japanese, and emojis in a mailbox, but I wouldn't expect many<br class="">
mail systems to deliver it and if they do deliver it I would expect<br class="">
all sorts of warnings.<br class="">
<br class="">
One of the glaring holes in the EAI documents is that there is no<br class="">
practical advice on choosing mailbox names. We have developed<br class="">
conventions for ASCII names that LDH are fine, dots and plus signs and<br class="">
maybe apostrophes are OK, upper and lower case ASCII are generally<br class="">
interchagable, and beyond that you take your chances. We need<br class="">
appropriate guidance for mailbox names. <br class="">
<br class="">
Before anyone suggests it, the rule for mailboxes can NOT be the same<br class="">
as for IDNs, since a dot is not a separator, mailboxes have always<br class="">
allowed characters not allowed in hostnames, and mail systems have<br class="">
always done fuzzy matching to allow misspellings that wouldn't be<br class="">
possible in domain names.<br class="">
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The IETF's PRECIS working group has advice on identifiers that would<br class="">
be a good place to continue from. I don't know if the IETF has the<br class="">
energy to do that, or if people here could usefully contribute.<br class="">
<br class="">
R's,<br class="">
John<br class="">
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🌏 🌍 🌎<br class="">
André Schappo<br class="">
<a href="mailto:%E5%B0%8F%E5%B1%B1@%E7%94%B5%E9%82%AE.%E5%9C%A8%E7%BA%BF?Subject=%E4%BD%A0%E5%A5%BD%E5%B0%8F%E5%B1%B1%F0%9F%98%9C" class="">小山@电邮.在线?Subject=你好小山😜</a><br class="">
<a href="https://schappo.blogspot.co.uk" class="">schappo.blogspot.co.uk</a><br class="">
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