Are Email Addresses Case Sensitive?

Every email address has two parts that are separated by the @ sign: the username and the domain from which the email account was created. Both sides typically contain both upper-case and lower-case letters and may contain numbers, underscores, or periods. It's easy to make an error when typing an email address, and it's important to use the proper lower-case and upper-case letters.

Is recipient@example.com the same as Recipient@EXAMPLE.com as far as email servers are concerned?

The domain name in an email address is case insensitive, meaning the case doesn't matter. The username, however, is case sensitive. The email address recipient@example.com is different than Recipient@example.com. However, the email address recipient@EXAMPLE.com is the same as recipient@example.com.

Because the case sensitivity of email addresses can create confusion and interoperability problems, some email providers and clients either fix the case if the email address is typed wrong or ignore the case. Not many email services or ISPs enforce case sensitive email addresses. This means that if the address is typed wrong, it's likely to be delivered.