Subject: Re: bug#22754: 25.1.50; Rmail does not follow RFC 2822

From: Glenn Morris <[email-masked]>
Date: Sat, 27 Feb 2016 22:04:18 -0500

Marcin Borkowski wrote:

> I've been told that if it is not stated explicitly that field names are
> case-insensitive, they are not, and their names should nit be changed in
> any way.
>
>>     1.2.2. Syntactic notation
>>     
>>     Characters will be specified either by a decimal value (e.g., the value
>>     %d65 for uppercase A and %d97 for lowercase A) or by a case-insensitive
>>     literal value enclosed in quotation marks (e.g., "A" for either
>>     uppercase or lowercase

There's nothing in the RFC that supports what you were told.
Where it says anything, it says the opposite, as I cited.
The situation is the same in the later RFC 5322.
See also the more explicit RFC 5234:

  ABNF strings are case insensitive and the character set for these
  strings is US-ASCII.
  [...]
  To specify a rule that is case sensitive, specify the characters
  individually.

Any sane mail app should be prepared for "CC:", "Cc:", "cc:", or even
"cC:".