Stephen John Smoogen wrote:
On 7 September 2017 at 16:07, Alexander Dalloz <ad+lists@xxxxxxxxx> wrote:
Am 07.09.2017 um 20:07 schrieb hw:
Gordon Messmer wrote:
On 09/07/2017 08:11 AM, Stephen John Smoogen wrote:
This was always
problematic because DNS hostnames and email addresses in the RFC
standards were case insensitive
Not quite. SMTP is required to treat the "local-part" of the RCPT
argument as case-sensitive, and to preserve case when relaying mail. The
destination is allowed to treat addresses according to local policy, but in
general SMTP is case sensitive with regard to the user identifier.
Last time I checked, RFCs said that local parts *should not* be case
sensitive,
and cyrus defaulted to treat them case sensitive, which is a default that
usually
needs to be changed because senders of messages tend to not pay any
attention to
the case sensitiveness of recipient addresses at all, which then confuses
them like
any other error.
The relevant part from the RFC:
https://www.ietf.org/rfc/rfc5321.txt
2.4. General Syntax Principles and Transaction Model
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.
for maximum interoperability, a host that expects to receive mail
SHOULD avoid defining mailboxes where the Local-part requires (or
uses) the Quoted-string form or where the Local-part is case-
sensitive.
Thanks for the clarification to my original email. I misremembered
RFC821 and thought it was for the entire part..
Commands and replies are not case sensitive. That is, a command or
reply word may be upper case, lower case, or any mixture of upper and
lower case. Note that this is not true of mailbox user names. For
some hosts the user name is case sensitive, and SMTP implementations
must take case to preserve the case of user names as they appear in
mailbox arguments. Host names are not case sensitive.
RFC2821, section 4.1.2:
" for maximum interoperability, a host that expects to receive mail
SHOULD avoid defining mailboxes where the Local-part requires (or
uses) the Quoted-string form or where the Local-part is case-
sensitive.
"
It comes down to that case-preservation is demanded from the implementations
of protocols while, pragmatically, local parts are encouraged to be case
insensitive.
More than a decade ago, I argued that the default used by cyrus be changed to
treat local parts case insensitve. About 2 years ago, that still hadn´t
changed.
So everyone deploying cyrus, be aware. Other than that, cyrus always worked
flawlessly, and I highly recommend it to everyone needing an IMAP server.
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