Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2004).

Abstract

This registers seven new mail transmission types (ESMTPA, ESMTPS, ESMTPSA, LMTP, LMTPA, LMTPS, LMTPSA) for use in the "with" clause of a Received header in an Internet message.

この文書は、インターネット・メッセージの Received 頭の with の項で使用する7つの新しいメイル転送型 (ESMTPA, ESMTPS, ESMTPSA, LMTP, LMTPA, LMTPS, LMTPSA) を登録します。

1. IANA Considerations

As directed by SMTP [2], IANA maintains a registry [7] of "WITH protocol types" for use in the "with" clause of the Received header in an Internet message. This registry presently includes SMTP [6], and ESMTP [2]. This specification updates the registry as follows:

SMTP が示す通り、 IANA はインターネット・メッセージの Received 頭の with の項で使用する「WITH プロトコル型」 の登録簿を管理しています。この登録簿は現在 SMTP と ESMTP を含んでいます。 この仕様書は登録簿を次の通り更新します。

• o The new keyword "ESMTPA" indicates the use of ESMTP when the SMTP AUTH [3] extension is also used and authentication is successfully achieved.
• o The new keyword "ESMTPS" indicates the use of ESMTP when STARTTLS [1] is also successfully negotiated to provide a strong transport encryption layer.
• o The new keyword "ESMTPSA" indicates the use of ESMTP when both STARTTLS and SMTP AUTH are successfully negotiated (the combination of ESMTPS and ESMTPA).
• o The new keyword "LMTP" indicates the use of LMTP [4].
• o The new keyword "LMTPA" indicates the use of LMTP when the SMTP AUTH extension is also used and authentication is successfully achieved.
• o The new keyword "LMTPS" indicates the use of LMTP when STARTTLS is also successfully negotiated to provide a strong transport encryption layer.
• o The new keyword "LMTPSA" indicates the use of LMTP when both STARTTLS and SMTP AUTH are successfully negotiated (the combination of LSMTPS and LSMTPA).
• o The references for the ESMTP and SMTP entries in the registry should be updated to the latest specification [2] since both RFC 821 and RFC 1869 [5] are obsoleted by RFC 2821.

• 新しい鍵語 ESMTPA は ESMTP の使用時で SMTP AUTH 拡張も使用していて認証が成功していることを示します。
• 新しい鍵語 ESMTPS は ESMTP の使用時で STARTTLS も強い輸送暗号層を提供する折衝に成功していることを示します。
• 新しい鍵語 ESMTPSA は ESMTP の使用時で STARTTLS と SMTP AUTH の両方の折衝に成功していること (ESMTPS と ESMTPA の組合せ) を示します。
• 新しい鍵語 LMTP は LMTP の使用を示します。
• 新しい鍵語 LMTPA は LMTP の使用時で SMTP AUTH 拡張も使用していて認証が成功していることを示します。
• 新しい鍵語 LMTPS は ESMTP の使用時で STARTTLS も強い輸送暗号層を提供する折衝に成功していることを示します。
• 新しい鍵語 LMTPSA は ESMTP の使用時で STARTTLS と SMTP AUTH の両方の折衝に成功していること (LMTPS と LMTPA の組合せ) を示します。
• 登録簿の ESMTP と SMTP の項目の参照は、 RFC 821 も RFC 1869 も RFC 2821 で廃止されたので、最新の仕様書に更新するべきです。

2. Implementation Experience

The ESMTPA, ESMTPS and ESMTPSA keywords have been implemented in deployed email server software for several years and no problems have been reported with their use.

鍵語 ESMTPA, ESMTPS, ESMTPSA は実際の電子メイル鯖で数年間実装されてきましたが、 これらの使用に関しての問題は何も報告されていません。

3. Security Considerations

Use of these additional keywords provides trace information to indicate when various high-level security framing protocols are used for hop-to-hop transport of email without exposing details of the specifics of the security mechanism. This trace information provides an informal way to track the deployment of these mechanisms on the Internet and can assist after-the-fact diagnosis of email abuse.

これらの追加の鍵語は、電子メイルのホップ毎輸送でいつ種々の高層保安枠付けプロトコルが使用されたかを、 保安機構の具体的な詳細を明らかにせずに示す追跡情報を提供します。 この追跡情報はインターネット上でのこうした機構の採用を追跡する非公式な方法を提供しますし、 電子メイル乱用の事後診断の助けとなり得ます。

These keywords are not normally protected in transport which means they can be modified by an active attacker. They also do not indicate the specifics of the mechanism used, and therefore do not provide any real-world security assurance. They should not be used for mail filtering or relaying decisions except in very controlled environments. As they are both cryptic and hidden in trace headers used primarily to diagnose email problems, it is not expected they will mislead end users with a false sense of security. Information with a higher degree of reliability can be obtained by correlating the Received headers with the logs of the various Mail Transfer Agents through which the message passed.

これらの鍵語は通常輸送路上で保護されていません。 つまり、活性攻撃者が修正できることを意味します。 また、使用した保安機構の具体的なことも示していませんから、 実世界の安全を保証してもいません。ですから、 非常に統率された環境以外ではメイル濾過や中継の決定に使用するべきではありません。 これらの鍵語は主として電子メイルの問題の診断に使用される追跡頭に暗号的に隠してありますから、 末端利用者が誤った意味の安全と誤解してしまうことはないでしょう。 高度な信頼性のある情報は、 Received 頭をメッセージが通過してきた種々のメイル転送エージェントの記録と照合することで得ることができます。

The trace information provided by these keywords and other parts of the Received header provide a significant benefit when doing after-the-fact diagnosis of email abuse or problems. Unfortunately, some people in a misguided attempt to hide information about their internal servers will strip Received headers of useful information and reduce their ability to correct security abuses after they happen. The result of such misguided efforts is usually a reduction of the overall security of the systems.

これらの鍵語や Received 欄の他の部分が提供する追跡情報は、 電子メイルの乱用や問題を事後診断する時に極めて有益です。 残念なことに、内部鯖の情報を隠そうとして誤った試みをする人がいて、 有用な情報の Received 頭を落として、 乱用が行われた後に修正する能力を削減しています。 このような誤った努力の結果は通常システム全体の保安を脆くしてしまいます。

4. References

Author's Address

   Chris Newman
   Sun Microsystems
   1050 Lakes Drive
   West Covina, CA  91790
   US

   EMail: chris.newman@sun.com

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