nope, email addresses are not case sensitive, however Web links (URL's) are.  The only part of email that is case sensitive is your own password.

Not for its email addresses, no.

gmail is even stranger, actually. They don't really care about periods, so, for example, [email protected] and [email protected] is the same thing

see link

I guess I am old school - I was taught each email address was unique...  

But I like Google's thinking here... it is still unique address, they just gave you infinite 'aliases'...

Everything preceding the '@' is governed by the rules imposed by the local systems handling email for that domain.  In the past, when the internet was predominantly infested with just geeks, most rules were to be case sensitive.  As more and more 'normal folk' came on it became increasingly obvious that case-sensitivity on that part of the address caused more problems than it solved.  Who wants their email bouncing because someone send it to [email protected] instead of [email protected] ?

Hence, the solution is to create another internet that is invite-only for Geeks! lol It'll take 10 minutes to perform a search because of all the rules and tricks involved, but it will be worth it!