You have to be a bit careful with that kind of argument though. According to the specs the local part of an email address (before the @) can also be case sensitive so [email protected] and [email protected] could be different email addresses. In the early days of a new system we implemented account email addresses following what the rules really say and making no assumptions. We then spent way too much time dealing with users who signed up with one address but then tried to log in with a "different" one because they had caps lock on or some auto-capitalisation feature in whatever browser they were using. Lesson learned - users do assume those are all the same address and cleaning up a database that sometimes has accounts for both [email protected] and [email protected] isn't much fun.