For years (if not decades) case haven’t been important in file names nor URL in the Microsoft world (using web server on a MS computer will result as this exact experience concerning letter case. An Image.jpg or IMAGE.JPG will only show one of the two images).
SMTP RFC 2821 says that the local part of the email address is case sensitive. Some ignore this and consider upper and lower case the same.
Section 2.4:
> 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.
What it means is, a mailserver should resolve local part case-insensitively, so that Bob@example.com and bob@example.com end up in the same mailbox.
But, to be spec-compliant, a mailserver MUST send on an email addressed to AlIcE@example.net to AlIcE@example.net, exactly, without downcasing it to alice@example.net.
I'd imagine this is often honored in the breach, but there you have it.
Could this be an extension of that ? Looks like.