On 29 Jul 2015, at 18:56, David B Funk wrote:
IE the DNS system is always case-insensitive and most systems are too
WRT
the email ID.
Does this text look at all familiar?
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.
The difference between DNS being specified as case-insensitive and SMTP
being specified as case-preserving is non-trivial. There's nothing wrong
with a domain having a case-squashed local namespace, in fact I am in
total agreement with that as the most prudent policy for the
overwhelming majority of mail domains. However, the best way to get a
measurement of how widespread case-sensitive mail domains are is to
ignore those RFC "MUST" statements and proliferate the use of tools
which intentionally case-squash local-parts in domains about which their
users are purely ignorant and use the result to reject or drop mail.
Arguably, this experiment needs doing just to generate data on whether
that antique RFC provision remains necessary.
