Hi Ted,

On 26 Feb 2016, at 10:39 am, Theodore Petrosky <[email protected]> wrote:

> I’ve been following this conversation, quite interesting. But, and this is 
> just a question for the conversation. Is there any reason when the user 
> registers that the user name (email address) isn’t folded into lowercase and 
> stored that way?

To be honest, that would probably work most of the time, possibly all of the 
time. Here’s where I address the theoretical problem with it in the original 
post:

> 2. Although the domain part of an email address is case-insensitive, my 
> understanding is that the relevant RFCs suggest that you shouldn’t make 
> assumptions about the local part. While everything I’ve read claims that in 
> practice it will make no difference, let’s assume that we need to preserve 
> the address as entered at sign-up. (It’s fail-safe to do so, whether we 
> strictly need to or not.)


Domain names are case-insensitive. So if I sign up with ‘[email protected]’ 
and you store ‘[email protected]’, there’s no problem—when you send me an 
email, I will receive it. My understanding is that the relevant RFCs say, in 
summary, that you shouldn’t make any assumptions about the local part. So if I 
sign up with ‘[email protected]’, and you store ‘[email protected]’, you 
can’t _assume_ that will be delivered (even though it probably will be). Even 
if the RFCs said explicitly that the local part was case-insensitive, you’re 
relying on every MDA to implement that correctly. I don’t know of an example 
MDA that is case-sensitive on the local part, but that doesn’t mean there isn’t 
one.

So, the fail-safe approach is to store what the user signed up with, and use 
that as the literal email address when sending out email. As a nice UX 
enhancement, at login time we want to make a case-insensitive comparison 
between what the user enters in the textfield and what’s stored in the 
database. It’s the latter problem we’re trying to solve here.


-- 
Paul Hoadley
http://logicsquad.net/



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