[MlMt] Case sensitivity in address pattern matching

[Bill Cole]

On 6 May 2018, at 16:21 (-0400), Billy Youdelman wrote:

> On 6 May 2018, at 12:30 MST, Randall Gellens wrote:
>
>> I have address patterns set for my accounts, and discovered that when 
>> a sender has an address for me in all upper case, MM does not 
>> recognize it as matching the address pattern.
>
> Call me crazy, I don't care, but ...
>
> If this is actually a problem that needs a solution, I would like to 
> strongly suggest that forcing entire email addresses to lower-case is 
> not it.

It is a problem that needs some solution, because the local part of an 
email address MAY be case-sensitive but usually is not. Complicating 
that, 'postmaster' is ALWAYS case-insensitive, even on the rare mail 
system that otherwise supports case-sensitive local parts.

The domain part of an email address is NEVER case-sensitive. The 
canonical form of any non-IDN domain name is with all letters lower 
case, so interop pretty much requires tolerance for others 
case-squashing domain names, since that is definitively "Not Wrong." 
(Which does not mean it is "Right.")

> This is one of the more annoying things going on these days.  For 
> example, try and find any third-party DNS provider that leaves 
> upper-case domain names alone.  Little things mean a lot.

As a technical matter, ASCII-label domain names are case-insensitive. It 
is a common practice for a nameserver to preserve the case of labels 
between queries and responses but it would be unsafe to depend on that 
behavior and outright wrong to provide different result data based on 
the case used in a query. DNSSEC depends on a definition of the 
canonical form of a domain name: all lower case.

> If I didn't want mine upper-cased I would not have written it that 
> way.

That's nice. To get case-sensitive domain names, you'll need to find a 
different Internet. :)



-- 
Bill Cole
bill at scconsult.com or billcole at apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Currently Seeking Steady Work: https://linkedin.com/in/billcole