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Are Email Addresses Case Sensitive?

It’s popular belief that email addresses are not case sensitive and so sending an email [email protected] will be delivered to the same recipient as [email protected] The chances are that using either of these addresses will result in the correct recipient receiving the email, according to standards however this does not always have to be the case.

Email addresses are broken down into 3 sections ‘localmailboxname’’@’’’. The local mailbox name section of the email is in fact case sensitive, so emailing [email protected] could have a different recipient to [email protected] The domain name section however is not case sensitive (insensitive), emailing @DOMAINNAME.COM, or @DoMaInNaMe.CoM would all reach the same mailbox, assuming the names of the local mailboxes were identical.

This standard falls under RFC2821 which states that ‘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.’

This standard is in place, however most internet and email service providers do not adhere to the rule strictly. As long as the characters are correct in all parts of the address the service provider is likely to redirect any incorrect email addresses to the correct mailbox, regardless of their case. This is where the wide regard that emails addresses are not case sensitive has sprung.


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