Hi Dave,
Dave Thaler wrote:
Andrew Sullivan asked:
I'd be especially interested in whether people think that table is worth
anything, before I complete it. I'm of two minds.
I'd say yes.
To its credit, it made me go look at one of the reviews (Alexey's review of
RFC4314 at http://www.ietf.org/mail-archive/web/precis/current/msg00086.html)
for more info. I'm not that familiar with IMAP or SASLprep so I am confused
about
one thing and hope someone can explain it in simple terms for me :)
The review says:
Most likely case sensitive. Exact requirements on
case-sensitivity/case-preservation
depend on a specific implementation, e.g. an implementation might treat all user
identifiers as case insensitive (or case insensitive for US-ASCII subset only).
But RFC 4013 says:
This profile is not intended for use in
preparing identity strings that are not simple user names (e.g.,
email addresses, domain names, distinguished names), or where
identity or password strings that are not character data, or require
different handling (e.g., case folding).
I don't think there is necessarily a contradiction. Case folding can be
applied as an extra step after RFC 4013 processing.
The table Andrew added has "a,d" (but not "i"). That would be correct if all
implementations agreed on the case sensitivity rules. And RFC 4013 says it's
not appropriate for things that aren't case sensitive.
So I'm confused about the part of the review saying:
"Exact requirements on case-sensitivity/case-preservation
depend on a specific implementation, e.g. an implementation might treat all user
identifiers as case insensitive (or case insensitive for US-ASCII subset only)."
Can someone elaborate on this?
Ok, let me try to elaborate on my review and why I wrote what I wrote. I
was talking specifically about IMAP/POP/SMTP usernames (passwords are
another story). Many email servers support all of the three protocols
and use the same identity format in all three. For a given email address
the corresponding user identity is either the left hand side of the
email address and/or the whole email address. (This isn't documented
anywhere, but it is one of the things that all email implementors need
to know.) The domain part (if included) is case-insensitive. SMTP (RFC
5321) says that the left hand side is case sensitive. In practice this
restriction turned out to be quite problematic in real deployments
(because humans just don't pay attention to case sometimes) and most of
the systems I know of treat left hand sides as case sensitive. However
until and unless an update to RFC 5321 declares that all left hand sides
of email addresses are case insensitive, we can't say that left hand
sides are always case insensitive, as some systems might rely on case
sensitivity of left hand sides.
Does this help?
Best Regards,
Alexey
--
Internet Messaging Team Lead, <http://www.isode.com>
JID: same as my email address
twitter: aamelnikov
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