[UA-discuss] interesting to note about emoji in mailbox name.

[John Levine]

In article <BYAPR21MB13171918C3D2AC0E8D177983D12F0 at BYAPR21MB1317.namprd21.prod.outlook.com> you write:
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>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.

First, I have to say that I am dismayed to see that many in the UASG
do not know that mailboxes and domain names are different and always
have been.  This is an important difference, and it's discussed at
some length in UASG 012.  This would probably be a good time for
everyone who hasn't read that document to read it now, so at least we
agree on the underlying facts.

As several people have pointed out, there are practically no rules for
what characters are technically legal in mailbox names, but that doesn't
mean that in practice you can put any junk in an address and expect it 
to work.  For example, this is a valid address:

  "); @,?~]"@m.jl.ly

but that doesn't mean I would hand it out as an address to anyone from
whom I wanted mail.

Similarly, you can technically put random combinations of Hindi,
Arabic, Japanese, and emojis in a mailbox, but I wouldn't expect many
mail systems to deliver it and if they do deliver it I would expect
all sorts of warnings.

One of the glaring holes in the EAI documents is that there is no
practical advice on choosing mailbox names.  We have developed
conventions for ASCII names that LDH are fine, dots and plus signs and
maybe apostrophes are OK, upper and lower case ASCII are generally
interchagable, and beyond that you take your chances.  We need
appropriate guidance for mailbox names.  

Before anyone suggests it, the rule for mailboxes can NOT be the same
as for IDNs, since a dot is not a separator, mailboxes have always
allowed characters not allowed in hostnames, and mail systems have
always done fuzzy matching to allow misspellings that wouldn't be
possible in domain names.

The IETF's PRECIS working group has advice on identifiers that would
be a good place to continue from.  I don't know if the IETF has the
energy to do that, or if people here could usefully contribute.

R's,
John