我对签名-milter 有疑问（http://www.signing-milter.org)。问题是 -b 标志是必需的，并且不建议使用 -b 标志，因为它会输出不符合 RFC 的电子邮件。但是，删除 -b 标志会导致邮件无法验证 S/MIME，并显示错误消息“内容被篡改”。-b 标志的描述如下：
Causes signing-milter to not break headerlines after a ; Header
lines moved inside a mime-container while signing must not be
longer then 76 characters. This switch disables the autobreak
before signing.
我尝试过只运行签名过滤器，也尝试过通过使用 MIME::Parser 解析邮件，然后从头开始重建电子邮件，从而“清除”邮件中的任何 RFC 错误。但仍然有些问题。以下邮件没有使用“清除”过滤器。
以下邮件使用以下命令正确签名：
signing-milter -g postfix -m /var/secure_files/cert/signers.cdb -s inet:9991 -t 60 -u postfix –b &>/dev/null </dev/null &
它将导致以下邮件被正确验证：
Return-Path: <[email protected]>
X-Original-To: [email protected]
Delivered-To: [email protected]
Received: from Bangatan601 (unknown [192.168.2.3])
by dns1.sebbe.eu (Postfix) with SMTP id E61E74C01D1
for <[email protected]>; Wed, 25 Feb 2015 11:12:41 +0100 (CET)
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=sebbe.eu; s=root;
t=1424859168; bh=0JJ2CUrz7gs1slXbxbBt0gped0s3PEJ2R6vh4blyqTQ=;
h=From:To:Subject:Date:From;
b=bxDrSPc8mTl7jSpHYlc3lDgPywm71Y8nnHFccVllB8yd8tYGh3lkPEQZhGxTTz+sn
iR8cto0qyBEZM8qNfgQSVD0a2jXdM38/VNB6G49Au252CZ6IsjfQdY9LFkdl7WudXt
YgYQ5Pnj59kCp4GSacRPHlwxQwZCT3hxwF5VcoPc=
Message-ID: <B385DB0CB2F144BFA9FE47A007A6B077@Bangatan601>
From: "Sebastian Nielsen" <[email protected]>
To: <[email protected]>
Subject: test
Date: Wed, 25 Feb 2015 11:12:39 +0100
MIME-Version: 1.0
X-Priority: 3
X-MSMail-Priority: Normal
Importance: Normal
X-Mailer: Microsoft Windows Live Mail 16.4.3528.331
X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3528.331
X-Hashcash: 1:26:150225:[email protected]::NrJAmsa7evEzktIr:000000000000000000000000000000000000000001h79K
Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg="sha-256"; boundary="----162A57F1542DDFAD76008518F14459BD"
This is an S/MIME signed message
------162A57F1542DDFAD76008518F14459BD
Content-Type: multipart/alternative; boundary="----=_NextPart_000_0019_01D050EB.F7C76180"
------=_NextPart_000_0019_01D050EB.F7C76180
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
test
------=_NextPart_000_0019_01D050EB.F7C76180
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<HTML><HEAD></HEAD>
<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">
<DIV>test</DIV></DIV></DIV></BODY></HTML>
------=_NextPart_000_0019_01D050EB.F7C76180--
------162A57F1542DDFAD76008518F14459BD
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
MIIJCwYJKoZIhvcNAQcCoIII/DCCCPgCAQExDzANBglghkgBZQMEAgEFADALBgkq
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CcshMBM62XZFtkQmNvT9
------162A57F1542DDFAD76008518F14459BD--
但是，如果我从 signature-milter 中删除 -b 标志，它将被签名如下：
signing-milter -g postfix -m /var/secure_files/cert/signers.cdb -s inet:9991 -t 60 -u postfix &>/dev/null </dev/null &
其结果是：
Return-Path: <[email protected]>
X-Original-To: [email protected]
Delivered-To: [email protected]
Received: from Bangatan601 (unknown [192.168.2.3])
by dns1.sebbe.eu (Postfix) with SMTP id 6CDFD4C0969
for <[email protected]>; Wed, 25 Feb 2015 10:58:00 +0100 (CET)
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=sebbe.eu; s=root;
t=1424858297; bh=g681Ani3vbnBMVPvXfhl81tk5PAU2QiaQD7wU8Opt0s=;
h=From:To:Subject:Date:From;
b=X4bAU3CenDkFk45IUztPl3sYkEWvOGphwAPBtGbdmtlUQ5Z5Faf1l/7B7Uz+J2lOu
tdyWgsJ4rHJk0+ZC+R/GxShyc8H9tPyUpinR9psIJJG4bHFmbkcoeykTMCzootnOxO
+GpHHPUHCwxaqBMDMfOKXgos691KZi++1LRsYThI=
Message-ID: <AA66989B33FB47379BEAE4365DE5394E@Bangatan601>
From: "Sebastian Nielsen" <[email protected]>
To: <[email protected]>
Subject: test
Date: Wed, 25 Feb 2015 10:57:53 +0100
MIME-Version: 1.0
X-Priority: 3
X-MSMail-Priority: Normal
Importance: Normal
X-Mailer: Microsoft Windows Live Mail 16.4.3528.331
X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3528.331
X-Hashcash: 1:26:150225:[email protected]::DwuKWYWY2MN+ZUXB:000000000000000000000000000000000000000003yEF8
Content-Type: multipart/signed;
protocol="application/pkcs7-signature";
micalg="sha-256";
boundary="----FD52A1653AA3980B5C0A3BE3D9993FAB"
This is an S/MIME signed message
------FD52A1653AA3980B5C0A3BE3D9993FAB
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_0007_01D050E9.E7B05740"
------=_NextPart_000_0007_01D050E9.E7B05740
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
test
------=_NextPart_000_0007_01D050E9.E7B05740
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<HTML><HEAD></HEAD>
<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">
<DIV>test</DIV></DIV></DIV></BODY></HTML>
------=_NextPart_000_0007_01D050E9.E7B05740--
------FD52A1653AA3980B5C0A3BE3D9993FAB
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
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0GAvKNW+4OrtIjzrCc8n
------FD52A1653AA3980B5C0A3BE3D9993FAB--
这不成立。（错误信息：内容被篡改）。
以下是来自同一客户端（Windows Live Mail）的一封未签名的邮件，可用于追踪任何 RFC 错误：
From: "Sebastian Nielsen" <[email protected]>
To: <[email protected]>
Subject: test
Date: Mon, 2 Mar 2015 23:17:33 +0100
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_0005_01D0553F.10373AE0"
X-Priority: 3
X-MSMail-Priority: Normal
Importance: Normal
X-Mailer: Microsoft Windows Live Mail 16.4.3528.331
X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3528.331
Det här är ett flerdelat meddelande i MIME-format.
------=_NextPart_000_0005_01D0553F.10373AE0
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
test
------=_NextPart_000_0005_01D0553F.10373AE0
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<HTML><HEAD></HEAD>
<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">
<DIV>test</DIV></DIV></DIV></BODY></HTML>
------=_NextPart_000_0005_01D0553F.10373AE0--
问题是什么？我在 Postfix 用户列表上询问，得到的答案是输入不符合 RFC 标准，但具体是哪方面呢？（所以我可以在此之前添加内容过滤器来解决这个问题）。该邮件是由 Windows Live Mail 创建的。
答案1
我在 Outlook 2013 和 Outlook 2016 中看到了完全相同的行为，两者都错误地将经过签名的混合签名多部分邮件报告为已篡改，The Bat! v7 Professional（Windows）和 Mac Mail（El Capitan）会将相同的邮件报告为有效邮件吗？
该问题是由于邮件负载末尾的回车符 (CR) 或换行符 (LF) 或两者的组合 (CRLF) 过多造成的。
消息有效负载的结束意味着最终：
------=_NextPart_000_0005_01D0553F.10373AE0--
在您发布的未签名/原始消息中。
无论哪个客户端发送消息，Outlook 到 Outlook 都会失败，就像 Mac Mail 到 Outlook 一样。
看到您使用 Windows Live Mail，这让我认为这会影响所有使用 Windows 邮件和/或加密后端的邮件客户端。
您甚至可以通过使用 telnet/ncat 发送多部分消息来可靠地重现此情况...
因此，在此要澄清的是，我几乎 99% 确信您的邮件已使用有效证书正确签名。这只是微软的做法——再次——不同而已。
现在我不知道-b我确信 switch 在签名 milter 中内部做了操作，以确保在签名之前你的有效载荷被正确地转义。
“Did” 只是因为这个选项似乎在当前版本中被删除了（此处运行的是签名 milter 版本 20150308），它只输出
由于兼容性原因，选项 -b 被忽略，你可以安全地将其删除
当使用此参数执行时，邮件当然仍然无法在 Outlook 中验证。
因此，最明显的解决方法似乎是将邮件通过额外的过滤器进行过滤，然后再将其发送到签名过滤器。
由于我已经有了这样一个自定义的 milter（使用 libmilter 用 python 编写），我可以简单地采用我的代码来解决这个问题：
...
if mail.is_multipart():
logging.debug("Stripping tailing line feeds (if any) from multi-part payload")
new_body = new_body.rstrip()
workflow["repl_body"] = new_body
return workflow
因此 Outlook 终于不再无谓的抱怨了。
干杯