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- and lower-case letters as well as numerals and underscores or periods. Considering how easy it is to make an error when typing an email address, you may be interested to know how important using lower-case letters versus upper-case ones really is. For example, is recipient@example.com the same as Recipient@EXAMPLE.com as far as email servers are concerned?

The domain name part of an email address is case insensitive, meaning the case doesn't matter. The username part, however, is case sensitive. The email address recipient@example.com is indeed different from Recipient@example.com.

However, since the case sensitivity of email addresses can create confusion, interoperability problems, and user aggravation, some email providers and clients either fix the case for you if you type it in wrong, or ignore the case altogether. In fact, hardly any email service or ISP enforces case sensitive email addresses. What that means for you is that, even if addresses you type an address in wrong, it's still likely to be delivered.