DKIM 签名是否应插入主题后：header？

Question

我的 ISP (Virgin Media) 在他们的电子邮件中介绍了 DKIM。

发送电子邮件后，我查看了源代码，发现他们将 DKIM 签名放在主题之间：header 和 body。

EstZLcTm/VjmbwAAeUlFJQ
    ; Thu, 25 May 2017 07:17:29 +0200
Received: from know-smtprelay-omc-3.server.virginmedia.net ([80.0.253.67])
    by mx6.tb.ukmail.iss.as9143.net with bizsmtp
    id QVHM1v00m1U0oNg01VHVUu; Thu, 25 May 2017 07:17:29 +0200
X-SourceIP: 80.0.253.67
X-CNFS-Analysis: v=2.2 cv=K/RSJ2eI c=1 sm=1 tr=0
 a=NusZbS+MIKNGTdhVDzOOtg==:117 a=o+HFlgnLNhdkn43EnkHUFQ==:17
 a=KXL61P45u2kA:10 a=tJ8p9aeEuA8A:10 a=MTPcje7z3XVcjakvMuAA:9
Received: from [192.168.0.19] ([80.193.xxxx.xxxx])
    by know-smtprelay-3-imp with bizsmtp
id QVHU1v0051httJ801VHU5a; Thu, 25 May 2017 06:17:29 +0100
X-Originating-IP: [80.193.182.78]
X-Authenticated-User: xxxxxxxxn@blueyonder.co.uk
X-Spam: 0
X-Authority: v=2.1 cv=XNzNMlVE c=1 sm=1 tr=0 a=o+HFlgnLNhdkn43EnkHUFQ==:117
 a=o+HFlgnLNhdkn43EnkHUFQ==:17 a=L9H7d07YOLsA:10 a=9cW_t1CCXrUA:10
 a=s5jvgZ67dGcA:10 a=MTPcje7z3XVcjakvMuAA:9
From: xxxxxxxx@blueyonder.co.uk
To: xxxxxxxx@timothydutton.co.uk, xxxxxxxx@blueyonder.co.uk
Subject: Sending via Python
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=blueyonder.co.uk;
    s=meg.feb2017; t=1495689449;
    bh=8bjk8lFzQ2833A/RBLNeoi8C+tOykYEwquKHC+57mNw=; h=From:To:Subject;
    b=ZuUwY74fd1AyxgXZ1LalJmb4fUFNqrQzOPall5FXrwTWoEYMBqR6u44HNJ1VOp1Jh
     +ik/ip8stBs7SXM/3ViaL/Vj4cP9CPdxO1UY/kblhojNF2Jw31f69gCpGdDQVCx6eC
     1KNdN0VadqQYVXd//wERGhXo+h2tkN2Ey0fZHxItXnN4ua90wwJfg3Iq2kM16m7OYw
     W+JiISTy84jqYxS7TFpgtfSLdZUG5y5OyG9r9rP9JBXxqBUIaq/QlAfcuTVJ9HXhLf
     h0d0CWLqSRoNrE2Dcqe/ES5cl12tL1HR3wHN4oU/kT0ilINEzRGSzkkeT0eHAUSjC6
     zfRok7vuo+GQA==

Yo this is a mail sent via Python 3.6

根据 Virgin Media 的说法，这是预期的行为。但我的理解是 SMTP 服务器应该将 header 添加到邮件的开头而不是中间？

SMTP 或 DKIM 标准是否允许这样做，或者它会导致问题吗？

Answer 1

是的，这是 DKIM 标准允许的。我知道的唯一要求如下：

The DKIM-Signature header field MUST be inserted before any other DKIM-Signature fields in the header block. RFC 6376 section 5.6

但是建议将其添加到消息中：

The DKIM-Signature header field SHOULD be treated as though it were a trace header field as defined in Section 3.6 of [RFC5322] and hence SHOULD NOT be reordered and SHOULD be prepended to the message. RFC 6376 section 3.5

DKIM 签名是否应插入主题后：header？

Should the DKIM signature be inserted after the Subject: header?

email

dkim