International email

International email (IDN email or Intl email) is email that contains international characters (characters which do not exist in the ASCII character set), encoded as UTF-8, in the email header and in supporting mail transfer protocols. The most significant aspect of this is the allowance of email addresses (also known as email identities) in most of the world's writing systems, at both interface and transport levels.

Traditional email addresses are limited to characters from the English alphabet and a few other special characters.

The following are valid traditional email addresses:

A Russian might wish to use дерек@екзампил.ком as their identifier but be forced to use a transcription such as derek@example.com or even some other completely unrelated identifier instead. The same is clearly true of Chinese, Japanese and many other nationalities that do not use Latin scripts, but also applies to users from non-English-speaking European countries whose desired addresses might contain diacritics (e.g. André or Płużyna). As a result, email users are forced to identify themselves using non-native scripts - or programmers of email systems must compensate for this by converting identifiers from their native scripts to ASCII scripts and back again at the user interface layer.

International email, by contrast, uses Unicode characters encoded as UTF-8 - allowing for the encoding the text of addresses in most of the world's writing systems. The following are all valid international email addresses:

Although the traditional format for email header section allows non-ASCII characters to be included in the value portion of some of the header fields using MIME-encoded words (e.g. in display names or in a Subject header field), MIME-encoding must not be used to encode other information in a header, such as an email address, or header fields like Message-ID or Received. Moreover, the MIME-encoding requires extra processing of the header to convert the data to and from its MIME-encoded word representation, and harms readability of a header section. Including Unicode characters in a header section using UTF-8 encoding eliminates these limitations and also the need to transmit additional encoding and character set information, as UTF-8 encoding will be assumed implicitly.

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