draft-yoneya-ima-downgrade-01 Downgrading mechanism for Internationalized Address (IMA) 20 Mar 2006 Yoshiro YONEYA Kazunori Fujiwara

Changes from -00 Added downgrade requirements section Separate downgrade into two parts –SMTP downgrading –Mail Header downgrading Introduced encapsulation method

Downgrading requirements (1/2) 1.Downgrading MUST be performed only once 2.Upgrading MUST be performed at minimized place SMTP envelope: final destination MTA (MDA) Mail header: recipient’s MUA 3.Downgrading and upgrading MUST be automated 4.Downgrading and upgrading MUST be easy and lightweight as it is possible to do with MTA like 8BITMIME encapsulation

Downgrading requirements (2/2) 5.Downgrade and upgrade method MUST be defined clearly 6.Downgrading and upgrading MUST preserve all header information 7.Downgrading MUST support sender authentication header checking such as SPF and/or DomainKeys/DKIM 8.Downgrading occurrence MUST be recorded

Downgrading Overview When SMTP session contains IMA, i.e. –SMTP Envelope contains IMA, and/or –Mail Header contains IMA/UTF-8 MUA/MTA decides downgrade or bounce –if SMTP server (next MTA) does not support “I ” Condition to downgrade is For all IMA, –Specified ALT-ADDR with US-ASCII address, or –Specified ATOMIC

SMTP Downgrading MTA replaces IMA with specified or generated alternative US-ASCII address –MTA generates alternative US-ASCII address if no ALT- ADDR option and ATOMIC "y“ is specified domain-part: Punycode/IDNA local-part: Punycode without normalization. Prefix MUST be assigned by IANA (which is not "xn--") Appends replaced information with IMA-Downgraded- From and IMA-Downgraded-To header to mail header part –IMA-Downgraded-From: –IMA-Downgraded-To:

Mail Header Downgrading Two alternatives –MIME encapsulation Introduced in downgrade-01 –Header conversion Introduced in downgrade-00

MIME encapsulation Introduction of new content-type –'Content-Type: Message/EAI‘ is assumed Encoding –Downgrade whole message to be MIME encoded and becomes new MIME part (Message/EAI) –Copy Date, Message-ID headers –Copy From, To, CC headers if possible or use envelope header as From, To Decoding –If mail message contains only one MIME part and its Content-Type is 'Message/EAI', it may be downgraded –If mail body’s message-id and MIME part’s message-id are the same, it is downgraded message –Treat MIME part as entire mail message This method can preserve all headers and easy to implement

Header conversion Define conversion method to US-ASCII for all headers which contains IMA Each header has its own downgrading method –Sender/Recipient address –Trace information –IDs –Others This method is hard to preserve original header information exactly –Also, hard to implement DomainKeys/DKIM