Post-Delivery Message Downgrading for Internationalized Email Messages
The Email Address Internationalization (SMTPUTF8) extension to SMTP allows Unicode characters encoded in UTF-8 and outside the ASCII repertoire in mail header fields. Upgraded POP and IMAP servers support internationalized messages. If a POP or IMAP client does not support Email Address Internationalization, a POP or IMAP server cannot deliver internationalized messages to the client and cannot remove the message. To avoid that situation, this document describes a mechanism for converting internationalized messages
Normative requirements
Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from. 0 must, 5 should, 0 may.
3.2.8 Other Header Fields
- SHOULDIf the software understands the header field's structure and a downgrading algorithm other than Unstructured is applicable, that software SHOULD use that algorithm; Unstructured downgrading is used when there is no other option.
5 Security Considerations
- SHOULD NOTThe downgrade mechanism SHOULD NOT remove signatures even if the signatures will fail validation after downgrading.
- SHOULDAs much of the information as possible from the original message SHOULD be preserved.
6 Implementation Note: Encoded-Word Encoding
- SHOULDWhile RFC 5322 states that implementations SHOULD limit lines to 78 characters or less, implementations MAY choose to allow overly long encoded words to work around faulty implementations of encoded-words.
- SHOULDImplementations that choose to do so SHOULD have an optional mechanism to limit line length to 78 characters.