On Apr 15, 2016, at 10:23 AM, Arnt Gulbrandsen
<arnt(_at_)gulbrandsen(_dot_)priv(_dot_)no> wrote:
John C Klensin writes:
Unless people propose to update RFC 5321 to eliminate a
requirement that has been in place from 821 and through 1123 and
2821, I don't see that there is anything to discuss. It seems
to me that the rules are very clear, i.e., that, except on the
final delivery SMTP server, two mailboxes are equal iff:
-- The domain parts are equal under DNS rules
(case-independent for ASCII strings and U-label:A-label
equivalence for IDNA strings)
-- The local parts are equal if they are octet-by-octet
identical.
If you ask people to type in their address in a web form, the addresses will
largely be typed in by people whose email addresses are case-insensitive, and
many of them know it. Rather like their names and street addresses, which
have proper casing but not essential casing.
You're suggesting that although the user may know the address to be
case-sensitive, the software used should absolutely not consider it
case-insensitive.
That sort of dissonance between user and software just isn't good.
"except on the final delivery server" is an important part of what John said.
While the message is in the realm of SMTP, it mustn't be modified, meaning that
two local parts are equivalent only if they're identical (I guess).
Once it leaves SMTP and hits the final delivery point, that can make any
changes, canonicalizations or comparisons it wants. Case-folding or
case-insensitive comparison is a common one.
Cheers,
Steve
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