Open Issue: Splitting of local-part into labels and where?

Hi!

The question of whether or not to split the dequoted local-part into 
labels and if so, at which delimiter characters, remains unanswered in 
the -00 draft.

I think that splitting into labels is needed to keep old software (esp. 
MTAs and filtering software) working. I can't add more to Roy's 
arguments here, and I feel there will be not much discussion about this 
particular issue.

The more interesting point is _where_ to split. There are some very 
obvious characters (mainly full stops and hyphens), but apart from 
that, the rest of the candidate chars is much less clear.

I'd include at least the following:
 @ [1]
 + (used for subaddresses)

The draft also mentions '!', Roy mentioned the underscore.

In addition, all such separators should be recognized in all their 
variants (for full-stops, see IDNA, for @ see draft, for others I admit 
to not know the Unicode repertoire by heart ;-)) and be replaced with 
their US-ASCII equivalents.

The draft also mentions the option of using all non-alnum US-ASCII 
characters. If the number of equivalent Unicode code points is small, 
then this is certainly the best option, although we should then provide 
a mapping table for the to-usascii mapping.

Marc

[1] Which reminds my that the draft specifies splitting local-part and 
domain at _the_ at-sign. It should probably read "at the _last_ 
at-sign", since local-parts may contain at-signs themselves.

-- 
It's one thing to accept a risk to your own data, but quite another to
standardize on something that imposes that risk on others, no matter
how unlikely you think it is that anything "really bad" will happen,
and no matter how desirable the outcome.  -- Bart Schaefer, on ietf-822

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