Unicode and email

Many email clients now offer some support for Unicode. Some clients will automatically choose between a legacy encoding and Unicode depending on the mail's content, either automatically^[1] or when the user requests it.^[2]

Technical requirements for sending of messages containing non-ASCII characters by email include

• encoding of certain header fields (subject, sender's and recipient's names, sender's organization and reply-to name) and, optionally, body in a content-transfer encoding
• encoding of non-ASCII characters in one of the Unicode transforms
• negotiating the use of UTF-8 encoding in email addresses and reply codes (SMTPUTF8)
• sending the information about the content-transfer encoding and the Unicode transform used so that the message can be correctly displayed by the recipient (see Mojibake).

If the sender's or recipient's email address contains non-ASCII characters, sending of a message requires also encoding of these to a format that can be understood by mail servers.