Are Email Addresses Case Sensitive?

Question: Are Email Addresses Case Sensitive?

Answer:

  • Yes, Email Addresses Are Case Sensitive.  But with a caveat.  First the caveat, almost no vendors or isps enforce the case sensitivity, but according to RFC 2821, the standard that defines how email transport works, lays down the law, saying that case must be preserved.  It goes on to say that it does not encourage case sensitivty.

Every email address has three parts. The username, what comes before the ‘@’, the ‘@’ itself and what follows the ‘@’, the domain name.

The answer to the question whether email addresses are case sensitive — whether it matters if you type ReCipiENt@eXaMPle.cOm or RECIPIENT@EXAMPLE.COM or recipient@example.com — has to do with these elements of an email address.

The domain name part of an email address is case insensitive (i.e. case does not matter). The username, however, is case sensitive. The email address ReCipiENt@eXaMPle.cOm is indeed different from recipient@example.com (but it the same as ReCipiENt@example.com).

But Case Typically Does Not Matter

Since the case sensitivity of email addresses can create a lot of confusion, interoperability problems and widespread headaches, it would be foolish to require email addresses to be typed with the correct case. Hardly any email service or ISP does enforce case sensitive email addresses, returning messages whose recipient’s email address was not typed correctly (in all upper case, for example).

This means that it does not typically matter what case you type an email address in when you send a message, but if recipient did give you an email address with distinct case, try to preserve it, however.

RFC 2821, the standard that defines how email transport works, lays down the email address case sensitivity issue thus:

The local-part of a mailbox MUST BE treated as case sensitive. Therefore, SMTP implementations MUST take care to preserve the case of mailbox local-parts. Mailbox domains are not case sensitive. In particular, for some hosts the user “smith” is different from the user “Smith”. However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.