Chances are that on at least one occasion you have wondered about email syntax, specifically case sensitivity. For example, you might have sent an email to your new on-line friend, ChunkyLover69@aol.com, and not been sure if you needed to capitalize the C and the L.
So, are email addresses case sensitive? The answer is, Yes but… Here’s how it works. There are three parts to an email address. The local mailbox part (ChunkyLover69@aol.com), the @, and the domain (ChunkyLover69@aol.com).
The domain is not case sensitive. It doesn’t matter if you type ChunkyLover69@aol.com, ChunkyLover69@AOL.COM, or ChunkyLover69@AoL.coM.
According to RFC 2821, the official standard for email addresses, the local mailbox part is case sensitive. So firstname.lastname@example.org, CHUNKYLOVER69@aol.com, and ChunkyLover69@aol.com are technically different addresses. This can cause some mix-ups when you type an email address, (and once in a while some problems between different types of computers), so RFC 2821 goes on to say that it’s a good idea to not strictly enforce this.
So here’s the bottom line. In practical use, it is rare for an email address to be case sensitive. However, if someone gives you their address with a mix of capital and lower case letters, than you should probably type it that way, at least the first time and until you know whether or not they’ll receive your email if you type the address differently.