[CentOS] login case sensitivity

[James B. Byrne]

On Thu, September 7, 2017 14:07, hw wrote:
> 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.
>
>

https://tools.ietf.org/html/rfc5321

Updated by: 7504                                        DRAFT STANDARD
                                                          Errata Exist
Network Working Group                                       J. Klensin
Request for Comments: 5321                                October 2008
Obsoletes: 2821
Updates: 1123
Category: Standards Track


. . .
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.
. . .

Case munging of the local part is handled by the local delivery agent
in my experience.  The Cyrus LMTP service can be, and often is,
configured to force lower case munging (imapd.conf
'lmtp_downcase_rcpt: 1') of the local part. That decision is site
specific.

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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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