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Traditional mail systems handle only ASCII characters in SMTP envelope and mail header fields. The Email Address Internationalization (UTF8SMTP) extension allows UTF-8 characters in SMTP envelope and mail header fields. To avoid rejecting internationalized Email messages when a server in the delivery path does not support the UTF8SMTP extension, some sort of converting mechanism is required. This document describes a downgrading mechanism for Email Address Internationalization. Note that this is a way to downgrade, not tunnel. There is no associated up-conversion mechanism, although internationalized email clients might use original internationalized addresses or other data when displaying or replying to downgraded messages.
1.
Introduction
2.
Terminology
3.
New header fields definition
3.1.
Envelope information preservation headers
3.2.
Address header field preservation headers
3.3.
Unknown header fields preservation headers
4.
SMTP Downgrading
4.1.
Path element downgrading
4.2.
ORCPT downgrading
5.
Email header fields downgrading
5.1.
Downgrading method for each ABNF element
5.1.1.
RECEIVED downgrading
5.1.2.
UNSTRUCTURED downgrading
5.1.3.
WORD downgrading
5.1.4.
COMMENT downgrading
5.1.5.
MIME-VALUE downgrading
5.1.6.
DISPLAY-NAME downgrading
5.1.7.
MAILBOX downgrading
5.1.8.
ENCAPSULATION downgrading
5.1.9.
TYPED-ADDRESS downgrading
5.2.
Downgrading method for each header field
5.2.1.
Address header fields which contain
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Traditional mail systems which are defined by [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.) and [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.) allow ASCII characters in SMTP envelope and mail header field values. The UTF8SMTP extension [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.), [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) and [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.) allows UTF-8 characters in SMTP envelope and mail header field values.
If an envelope address or header field contains non-ASCII characters, the message cannot be delivered unless every system in the delivery path supports UTF8SMTP. This document describes a downgrading mechanism to avoid rejection of such messages when a server which does not support the UTF8SMTP extension is encountered. Downgrading mechanism converts envelope and header fields to an all-ASCII representation.
[RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) allows UTF-8 characters to be used in mail header fields and MIME header fields. The downgrading mechanism specified here converts mail header fields and MIME header fields to ASCII.
This document does not change any protocols except by defining new header fields. It describes the conversion method from the internationalized email envelopes/messages which are defined in [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.) to the traditional email envelopes/messages which are defined in [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.) [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.).
[RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.) section 2.2 defines when downgrading occurs. If the SMTP client has an UTF8SMTP envelope or an internationalized message and the SMTP server doesn't support the UTF8SMTP SMTP extension, then the SMTP client MUST NOT send a UTF8SMTP envelope or an internationalized message to the SMTP server. The section shows 4 choices. The fourth choice is downgrading, as described here.
Downgrading may be implemented in MUAs, MSAs, MTAs which act as the SMTP client, or in MDAs, POP servers, IMAP servers which store or offer UTF8SMTP envelopes or internationalized messages to non-UTF8SMTP compliant systems which include message stores.
This document tries to define the downgrading process clearly and it preserves the original information as much as possible.
Downgrading in UTF8SMTP consists of the following four parts:
In Section 3 (New header fields definition), many header fields starting with "Downgraded-" are introduced. They preserve the original envelope information and the original header fields.
The SMTP downgrading is described in Section 4 (SMTP Downgrading). It generates ASCII only envelope information from an UTF8SMTP envelope.
The Email header fields downgrading is described in Section 5 (Email header fields downgrading). It generates ASCII only header fields.
The MIME header fields are expanded in [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.). The MIME header fields downgrading is described in Section 6 (MIME body part headers downgrading). It generates ASCII only MIME header fields.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
All specialized terms used in this specification are defined in the EAI overview [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) or in [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.)[RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.), MIME documents [RFC2045] (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) [RFC2183] (Troost, R., Dorner, S., and K. Moore, “Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field,” August 1997.) [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.). The terms "ASCII address", "internationalized email address", "non-ASCII address", "i18mail address", "UTF8SMTP", "message" and "mailing list" are used with the definitions from [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) document.
This document depends on [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.), [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.), and [RFC5337] (Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” September 2008.). Key words used in these document are used in this document, too.
The term "non-ASCII" is an UTF-8 string which contains at least one non-ASCII character.
An "UTF8SMTP envelope" has Email originator/recipient addresses expanded by [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.) and [RFC5337] (Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” September 2008.).
An "UTF8SMTP message" is Email messages expanded by [RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.).
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New header fields starting with "Downgraded-" are defined here to preserve those original envelope and header values which contain UTF-8 characters. During downgrading, one new "Downgraded-" header field is added for each original envelope or header field which cannot be passed as-is to a server which does not support UTF8SMTP. The original envelope or header field is removed or rewritten. Only those envelope and header fields which contain non-ASCII characters are affected. The result of this process is a message which is compliant with existing email specifications [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.) and [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.). The original internationalized information can be retrieved by examining the "Downgraded-" header fields which were added. Even though the information is not lost, the original message cannot be perfectly reconstructed. Hence, downgrading is a one-way process. However, an internationalized client might use the information in the "Downgraded-" header fields when processing a downgraded message, for example, such as displaying or composing a reply.
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SMTP envelope downgraded information <downgraded-envelope-addr> consists of the original non-ASCII address and the downgraded all-ASCII address.
downgraded-envelope-addr = [FWS] "<" [ A-d-l ":" ] uMailbox FWS "<" Mailbox ">" ">" [CFWS]
<uMailbox> is defined in [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.); <Mailbox> and <A-d-l> are defined in [RFC5321] (Klensin, J., “Simple Mail Transfer Protocol,” October 2008.), section 4.1.2.
Two headers "Downgraded-Mail-From:" and "Downgraded-Rcpt-To:" are defined to preserve SMTP envelope downgraded information. The header field syntax is specified as follows:
fields =/ downgradedmailfrom / downgradedrcptto downgradedmailfrom = "Downgraded-Mail-From:" unstructured CRLF downgradedrcptto = "Downgraded-Rcpt-To:" unstructured CRLF
The unstructured content is downgraded-envelope-addr treated as if it were unstructured with [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) encoding (and charset UTF-8) as needed.
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The address header fields preservation headers are defined to preserve the original header field. Their value field holds the original header field value. The header field syntax is specified as follows:
fields =/ known-downgraded-headers ":" unstructured CRLF known-downgraded-headers = "Downgraded-" original-headers original-headers = "From" / "Sender" / "To" / "Cc" / "Bcc" / "Reply-To" / "Resent-From" / "Resent-Sender" / "Resent-To" / "Resent-Cc" / "Resent-Bcc" / "Resent-Reply-To" / "Return-Path" / "Disposition-Notification-To"
Preserving a header field in a downgraded header field is defined as:
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The unknown header fields preservation headers are defined to encapsulate those original header fields which contain non-ASCII characters and are not otherwise provided for in the this specification. The encapsulation header field name is the concatenation of "Downgraded-" and the original name. The value field holds the original header field value.
The header field syntax is specified as follows:
fields =/ unknown-downgraded-headers ":" unstructured CRLF unknown-downgraded-headers = "Downgraded-" original-header-field-name original-header-field-name = field-name field-name = 1*ftext ftext = %d33-57 / ; Any character except %d59-126 ; controls, SP, and ; ":".
Encapsulating a header field in a "Downgraded-" header field is defined as:
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Target of downgrading elements in SMTP envelope are below:
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Downgrading the <path> of MAIL FROM and RCPT TO commands uses ALT-ADDRESS parameter defined in [RFC5336] (Yao, J. and W. Mao, “SMTP Extension for Internationalized Email Addresses,” September 2008.). A SMTP command is downgradable if the <path> contains non-ASCII address and the command has an ALT-ADDRESS parameter which specifies an ASCII address. Since only non-ASCII addresses are downgradable, specifying an ALT-ADDRESS value for an all-ASCII address is invalid for use with this specification, and no interpretation is assigned to it. This restriction allows for future extension of the specification even though no such extensions are currently anticipated.
Note that even if no downgrading is performed on the envelope, message header fields and message body MIME header fields that contain non-ASCII characters MUST be downgraded. This is described in Section 5 (Email header fields downgrading) and Section 6 (MIME body part headers downgrading).
When downgrading, replace each <path> which contains non-ASCII mail address with its specified alternative ASCII address and preserve the original information using "Downgraded-Mail-From" and "Downgraded-Rcpt-To" header fields as defined in Section 3 (New header fields definition). Before replacing, decode the ALT-ADDRESS parameter value because it is encoded as xtext [RFC3461] (Moore, K., “Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs),” January 2003.).
To avoid disclosing recipient addresses, the downgrading process MUST NOT add "Downgraded-Rcpt-To:" header if the SMTP downgrading targets multiple recipients. See Section 7 (Security considerations) for more detail.
As a result of the recipient address downgrading, the domain part of the recipient address prior to downgrading might be different from the domain part of the new recipient address. If the result of address resolution for the domain part of the new recipient address contains the server at the connection destination of the SMTP session for the recipient address prior to downgrading, the SMTP connection is valid for the new recipient address. Otherwise, the downgrading process MUST NOT send the downgraded message to the new recipient address via the connection and MUST try to send the downgraded message to the new recipient address.
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The "RCPT TO" command can have an ORCPT parameter if the DSN extension [RFC3461] (Moore, K., “Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs),” January 2003.) is supported. If the ORCPT parameter contains an "utf-8" type address and the address contains raw non-ASCII characters, the address MUST be converted to utf-8-addr-xtext form. Those forms are described in [RFC5337] (Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” September 2008.) and clarified by successor documents such as [I‑D.ietf‑eai‑dsnbis] (Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” December 2008.).
Before converting to utf-8-addr-xtext form, remove xtext encoding.
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This section defines the conversion method to ASCII for each header field which may contain non-ASCII characters.
[RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.) expands Received: header fields, [RFC5322] (Resnick, P., Ed., “Internet Message Format,” October 2008.) ABNF elements <mailbox>, <word>, <comment>, <unstructured>, [RFC2045] (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) ABNF element <value>.
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Header field downgrading is defined below for each ABNF element. Downgrading an unknown header field is also defined as ENCAPSULATION downgrading. Converting the header field terminates when no non-ASCII characters remain in the header field.
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If the header field name is "Received:" and the FOR clause contains a non-ASCII addresses, remove the FOR clause from the header field. Other parts (not counting <comment>s) should not contain non-ASCII values.
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If the header field has an <unstructured> field which contains non-ASCII characters, apply [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) encoding with charset UTF-8.
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If the header field has any <word> fields which contains non-ASCII characters, apply [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) encoding with charset UTF-8.
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If the header field has any <comment> fields which contains non-ASCII characters, apply [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) encoding with charset UTF-8.
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If the header field has any <value> elements defined by [RFC2045] (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,” November 1996.) and the elements contain non-ASCII characters, encode the <value> elements by [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.) with charset UTF-8 and the Language information empty. If the <value> element is <quoted-string> and it contains <CFWS> outside the DQUOTE, remove the <CFWS> before this conversion.
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If the header field has any <address> (<mailbox> and <group>) elements and they have <display-name> elements which contain non-ASCII characters, encode the <display-name> elements according to [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) with charset UTF-8. DISPLAY-NAME downgrading is the same algorithm as WORD downgrading.
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The <mailbox> elements have no equivalent format for non-ASCII addresses.
If the header field has any <mailbox> elements which contain non-ASCII characters,
preserve the header field in each Address header field preservation header defined in Section 3.2 (Address header field preservation headers),
and rewrite each <mailbox> element to ASCII only format.
The <mailbox> element which contains non-ASCII characters is one of three formats.
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if the header field contains non-ASCII characters
and for which no rule is given above,
encapsulate it in a Downgraded header field
described in Section 3.3 (Unknown header fields preservation headers)
as a last resort.
Applying this procedure to "Received" header field is prohibited.
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If the header field contains <utf-8-type-addr> and the <utf-8-type-addr> contains raw non-ASCII characters, it is utf-8-address form and convert it to utf-8-addr-xtext form as described in Section 4.2 (ORCPT downgrading). COMMENT downgrading is also performed in this case. If the address type is unrecognized and the header contains non-ASCII characters, then fall back to using ENCAPSULATION downgrading on the entire header.
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Header fields are listed in [RFC4021] (Klyne, G. and J. Palme, “Registration of Mail and MIME Header Fields,” March 2005.). This section describes the downgrading method for each header field.
If the whole mail header field does not contain non-ASCII characters, email header field downgrading is not required. Each header field's downgrading method is described below.
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- From:
- Sender:
- To:
- Cc:
- Bcc:
- Reply-To:
- Resent-From:
- Resent-Sender:
- Resent-To:
- Resent-Cc:
- Resent-Bcc:
- Resent-Reply-To:
- Return-Path:
- Disposition-Notification-To:
If the header field contains <mailbox> elements
which contains non-ASCII addresses,
preserve the header field in a downgraded header before the conversion.
Then perform COMMENT downgrading, DISPLAY-NAME downgrading and MAILBOX downgrading.
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- Original-Recipient:
- Final-Recipient:
If the header field contains non-ASCII characters, perform TYPED-ADDRESS downgrading.
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- Date:
- Message-ID:
- Resent-Message-ID:
- In-Reply-To:
- References:
- Resent-Date:
- Resent-Message-ID:
- MIME-Version:
- Content-ID:
- Content-Transfer-Encoding:
- Content-Language:
- Accept-Language:
- Auto-Submitted:
These header fields do not contain non-ASCII characters except in comments.
If the header contains UTF-8 characters in comments,
perform COMMENT downgrading.
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- Received:
perform COMMENT downgrading and RECEIVED downgrading.
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- Content-Type:
- Content-Disposition:
Perform MIME-VALUE downgrading and COMMENT downgrading.
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- Subject:
- Comments:
- Content-Description:
Perform UNSTRUCTURED downgrading.
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- Keywords:
Perform WORD downgrading.
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All other header fields which contains non-ASCII characters
are user-defined, missing from this draft
or future defined header fields.
Perform ENCAPSULATION downgrading.
If the software understands the header's structure and a downgrading
algorithm other than ENCAPSULATION is applicable, that software SHOULD use
that algorithm; ENCAPSULATION downgrading is used as a last resort.
Mailing list header fields (those that start in "List-")
are part of this category.
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MIME body part header fields may contain non-ASCII characters
[RFC5335] (Abel, Y., “Internationalized Email Headers,” September 2008.).
This section defines the conversion method to ASCII only header fields
for each MIME header field which contains non-ASCII characters.
Parse the message body's MIME structure for all levels and
check each MIME header field whether it contains non-ASCII characters.
If the header field contains non-ASCII characters in the header value,
the header is a target of the MIME body part headers downgrading.
Each MIME header field's downgrading method is described below.
COMMENT downgrading, MIME-VALUE downgrading, UNSTRUCTURED downgrading
are described in Section 5 (Email header fields downgrading).
- Content-ID:
- The Content-ID: header does not contain non-ASCII characters except in comments. If the header contains UTF-8 characters in comments, perform COMMENT downgrading.
- Content-Type:
- Content-Disposition:
- Perform MIME-VALUE downgrading and COMMENT downgrading.
- Content-Description:
- Perform UNSTRUCTURED downgrading.
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See "Security considerations" section in [RFC4952] (Klensin, J. and Y. Ko, “Overview and Framework for Internationalized Email,” July 2007.) for more discussion.
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While [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) has a specific algorithm to deal with whitespace in adjacent encoded-words, there are a number of deployed implementations that fail to implement the algorithm correctly. As a result, whitespace behavior is somewhat unpredictable in practice when multiple encoded words are used. While RFC 5322 states that implementations SHOULD limit lines to not more than 78 characters, implementations MAY choose to allow overlong encoded words in order to work around faulty [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.) implementations. Implementations that choose to do so SHOULD have an optional mechanism to limit line length to 78 characters.
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Downgrading is an alternative to avoid the rejection of messages which require UTF8SMTP support by a server which does not provide this. Implementing the full specification of this document is desirable, but a partial implementation is also possible.
If a partial downgrading implementation confronts an unsupported downgrading target, the implementation MUST NOT send the message to a server which does not support UTF8SMTP. Instead, it MUST reject the message or generate a notification of non-deliverability.
A partial downgrading, Trivial downgrading is discussed. It does not support non-ASCII addresses in SMTP envelope and address header fields, unknown header fields downgrading, the MIME body part headers downgrading. It supports
Otherwise, the downgrading fails.
Trivial downgrading targets mail messages which are generated by UTF8SMTP aware MUAs and contain non-ASCII characters in comments, display names, unstructured parts without using non-ASCII E-mail addresses. This mail message does not contain non-ASCII E-mail addresses in the SMTP Envelope and its header fields. But it is not deliverable via a UTF8SMTP un-aware SMTP server. Implementing full specification downgrading may be hard, but trivial downgrading saves mail messages without using non-ASCII addresses.
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The SMTP client may encounter a SMTP server which does not support the 8BITMIME SMTP extension [RFC1652] (Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker, “SMTP Service Extension for 8bit-MIMEtransport,” July 1994.). The server does not support "8bit" or "binary" data. Implementers need to consider converting "8bit" data to "base64" or "quoted-printable" encoded form and adjust the "Content-Transfer-Encoding" header field accordingly. If the body contains multiple MIME parts, this conversion MUST be performed for each MIME part.
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IANA is requested to register the following header fields in the
Permanent Message Header Field Repository, in accordance with the
procedures set out in [RFC3864] (Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields,” September 2004.).
- Header field name:
- Downgraded-Mail-From
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Rcpt-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-From
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Sender
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Cc
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Bcc
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Reply-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-From
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-Sender
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-Cc
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-Bcc
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Resent-Reply-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Return-Path
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
- Header field name:
- Downgraded-Disposition-Notification-To
- Applicable protocol:
- Status:
- experimental
- Author/change controller:
- IETF
- Specification document(s):
- This document (Section 3 (New header fields definition))
Furthermore, IANA is requested to refuse registration of all the field names that start with "Downgraded-" for unknown header fields downgrading described in Section 3.3 (Unknown header fields preservation headers) to avoid conflicts with existing IETF activity (Email Address Internationalization).
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Significant comments and suggestions were received from John Klensin, Harald Alvestrand, Chris Newman, Randall Gellens, Charles Lindsey, Marcos Sanz, Alexey Melnikov, Frank Ellermann, Edward Lewis, S. Moonesamy and JET members.
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This section is used for tracking the update of this document. Will be removed after finalize.
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[I-D.ietf-eai-dsnbis] | Newman, C. and A. Melnikov, “Internationalized Delivery Status and Disposition Notifications,” draft-ietf-eai-dsnbis-00 (work in progress), December 2008. |
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This section shows an SMTP Downgrading example. Consider a mail message where:
The example SMTP envelope/message is shown in Figure 1 (Original envelope/message (example 1)). In this example, the "To:" recipient's session is the focus.
MAIL FROM: <NON-ASCII-local@example.com> ALT-ADDRESS=ASCII-local@example.com RCPT TO: <NON-ASCII-remote1@example.net> ALT-ADDRESS=ASCII-remote1@example.net RCPT TO: <NON-ASCII-remote2@example.org> ------------------------------------------------------------- Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: DISPLAY-local <NON-ASCII-local@example.com <ASCII-local@example.com>> To: DISPLAY-remote1 <NON-ASCII-remote1@example.net <ASCII-remote1@example.net>> Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org> Date: DATE MAIL_BODY
Figure 1: Original envelope/message (example 1) |
In this example, there are two SMTP recipients, one is "To:", the other is "Cc:". The SMTP downgrading treats To: session downgrading. Figure 2 (SMTP Downgraded envelope/message (example 1)) shows SMTP downgraded example.
MAIL FROM: <ASCII-local@example.com> RCPT TO: <ASCII-remote1@example.net> ------------------------------------------------------------- Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com_?= =?UTF-8?Q?<ASCII-local@example.com>>?= Downgraded-Rcpt-To: =?UTF-8?Q?<NON-ASCII-remote1@example.net_?= =?UTF-8?Q?<ASCII-remote1@example.net>>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: DISPLAY-local <NON-ASCII-local@example.com <ASCII-local@example.com>> To: DISPLAY-remote1 <NON-ASCII-remote1@example.net <ASCII-remote1@example.net>> Cc: DISPLAY-remote2 <NON-ASCII-remote2@example.org> Date: DATE MAIL_BODY
Figure 2: SMTP Downgraded envelope/message (example 1) |
After SMTP downgrading, header fields downgrading is performed.
Final downgraded message is shown in Figure 3 (Downgraded message (example 1)).
Return-Path header will be added by the final destination MTA.
Return-Path: <ASCII-local@example.com> Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com_?= =?UTF-8?Q?<ASCII-local@example.com>>?= Downgraded-Rcpt-To: =?UTF-8?Q?<NON-ASCII-remote1@example.net_?= =?UTF-8?Q?<ASCII-remote1@example.net>>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?= From: =?UTF-8?Q?DISPLAY-local?= <ASCII-local@example.com> Downgraded-From: =?UTF-8?Q?DISPLAY-local_<NON-ASCII-local@example.com_?= =?UTF-8?Q?<ASCII-local@example.com>>?= To: =?UTF-8?Q?DISPLAY-remote1?= <ASCII-remote1@example.net> Downgraded-To: =?UTF-8?Q?DISPLAY-remote1_?= =?UTF-8?Q?<NON-ASCII-remote1@example.net_<ASCII-remote1@example.net>>?= Cc: =?UTF-8?Q?DISPLAY-remote2?= Internationalized address =?UTF-8?Q?NON-ASCII-remote2@example.org?= removed:; Downgraded-Cc: =?UTF-8?Q?DISPLAY-remote2_?= =?UTF-8?Q?<NON-ASCII-remote2@example.org>?= Date: DATE MAIL_BODY
Figure 3: Downgraded message (example 1) |
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In many cases, the sender wants to use non-ASCII address and the recipient is a traditional mail user. The SMTP server handing mail for the recipient and/or the recipient's MUA does not support UTF8SMTP extension. Consider a mail message where:
The second example envelope/message is shown in Figure 4 (Original message (example 2)).
MAIL From: <NON-ASCII-local@example.com> ALT-ADDRESS=ASCII-local@example.com RCPT TO: <ASCII-remote1@example.net> ------------------------------------------------------------- Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: DISPLAY-local <NON-ASCII-local@example.com <ASCII-local@example.com>> To: DISPLAY-remote1 <ASCII-remote1@example.net> Date: DATE MAIL_BODY
Figure 4: Original message (example 2) |
In this example, SMTP session is downgradable. Figure 5 (SMTP Downgraded envelope/message (example 2)) shows SMTP downgraded envelope/message.
MAIL From: <ASCII-local@example.com> RCPT TO: <ASCII-remote1@example.net> ------------------------------------------------------------- Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com_?= ?=UTF8?Q?<ASCII-local@example.com>>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: NON-ASCII-SUBJECT From: DISPLAY-local <NON-ASCII-local@example.com <ASCII-local@example.com>> To: DISPLAY-remote1 <ASCII-remote1@example.net> Date: DATE MAIL_BODY
Figure 5: SMTP Downgraded envelope/message (example 2) |
After SMTP downgrading, header fields downgrading is performed.
The downgraded example is shown in Figure 6 (Downgraded message (example 2)).
Return-Path: <ASCII-local@example.com> Downgraded-Mail-From: =?UTF-8?Q?<NON-ASCII-local@example.com_?= =?UTF8?Q?<ASCII-local@example.com>>?= Message-Id: MESSAGE_ID Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Subject: =?UTF-8?Q?NON-ASCII-SUBJECT?= Downgraded-From: =?UTF-8?Q?DISPLAY-local_<NON-ASCII-local@example.com_?= =?UTF-8?Q?<ASCII-local@example.com>>?= From: =?UTF-8?Q?DISPLAY-local?= <ASCII-local@example.com> To: =?UTF-8?Q?DISPLAY-remote1?= <ASCII-remote1@example.net> Date: DATE MAIL_BODY
Figure 6: Downgraded message (example 2) |
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Kazunori Fujiwara (editor) | |
JPRS | |
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda | |
Chiyoda-ku, Tokyo 101-0065 | |
Japan | |
Phone: | +81 3 5215 8451 |
Email: | fujiwara@jprs.co.jp |
Yoshiro YONEYA (editor) | |
JPRS | |
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda | |
Chiyoda-ku, Tokyo 101-0065 | |
Japan | |
Phone: | +81 3 5215 8451 |
Email: | yone@jprs.co.jp |