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3. Changes to RFC 5322

This specification extends the header syntax defined in RFC 5322 [RFC5322] to allow UTF-8 characters.

3.1. UTF-8 Syntax and Normalization​

UTF-8 characters can be used in the header fields as defined in the following sections. All UTF-8 strings MUST be valid UTF-8.

3.2. Syntax Extensions to RFC 5322​

The following rules are extended in ABNF [RFC5234] to allow UTF-8 characters.

VCHAR   =/  UTF8-non-ascii

ctext   =/  UTF8-non-ascii

atext   =/  UTF8-non-ascii

qtext   =/  UTF8-non-ascii

text    =/  UTF8-non-ascii

dtext   =/  UTF8-non-ascii

Where UTF8-non-ascii is defined as any UTF-8 character that is not an ASCII character.

3.3. Use of 8-bit MIME in Headers​

The 8-bit MIME extension [RFC6152] is used to allow 8-bit data in the body of the message. This specification extends that to allow 8-bit data in the headers as well.

3.4. Address Syntax​

The syntax for email addresses is extended to allow UTF-8 characters in the local-part and the domain part.

3.5. Trace Field Syntax​

Trace fields, such as Received, are extended to allow UTF-8 characters.

3.6. Message Header Body Syntax​

The syntax for the message header is extended to allow UTF-8 characters in the field names and field bodies.