[Users] Address book defaults to lower case

Andrej Kacian andrej at kacian.sk
Wed Mar 22 11:55:35 CET 2017

On Wed, 22 Mar 2017 10:11:25 +0000
Brian Morrison <bdm at fenrir.org.uk> wrote:

> On Wed, 22 Mar 2017 10:34:06 +0100
> wwp wrote:
> > I can't believe a server wants capitalized names in email addresses
> > (or case sensitiveness in general). Would you show us the error
> > thrown by this server?
> Actually folks, the local part of the address before the @ should have
> case preserved, there are people who do use capitalized addresses in
> this way.

You are both correct and incorrect (as is frequently the case with

RFC 2821[1] manages to contradict itself. In section 2.4, it says:

   [...] 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.  Mailbox
   domains are not case sensitive.  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.

Then later, in section 4.1.2:

   While the above definition for Local-part is relatively permissive,
   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-

Arguably, "MUST" takes precedence over "SHOULD".

1. https://tools.ietf.org/html/rfc2821


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