On Sat, Nov 21, 2009 at 07:04:25AM -0500, Jerry wrote:
> I was, perhaps incorrectly, of the opinion that case was not relevant
> in e-mail addresses. I thought that there was an RFC that mentioned
> this; although I cannot find one that specifically mentions case
> folding on the reply to address.
Message handling systems MUST preserve case, systems delivering messages
to a mailbox SHOULD ignore case.
> Is Yahoo's claim correct or are they simply trying to cover up for a
> problem on their end?
Their claim is not wrong, but it is wiser to design systems that avoid
this problem.
RFC 5321 Section 2.4
Verbs and argument values (e.g., "TO:" or "to:" in the RCPT command
and extension name keywords) are not case sensitive, with the sole
exception in this specification of a mailbox local-part (SMTP
Extensions may explicitly specify case-sensitive elements). That is,
a command verb, an argument value other than a mailbox local-part,
and free form text MAY be encoded in upper case, lower case, or any
mixture of upper and lower case with no impact on its meaning. The
local-part of a mailbox MUST BE treated as case sensitive.
Therefore, SMTP implementations MUST take care to preserve the case
of mailbox local-parts. In particular, for some hosts, the user
"smith" is different from the user "Smith". However, exploiting the
case sensitivity of mailbox local-parts impedes interoperability and
is discouraged. Mailbox domains follow normal DNS rules and are
hence not case sensitive.
--
Viktor.
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