在 Thunderbird 中对嵌入的电子邮件图像使用 Content-ID 和 cid
Using Content-ID and cid for embedded email images in Thunderbird
我在 PHP 应用程序中生成电子邮件，该应用程序将多个文件附加到 HTML 电子邮件。有些文件是 Excel 电子表格，有些文件是需要嵌入到 HTML 中的公司徽标，因此它们默认加载时使用 Content-ID 和 cid 标识符来引用附加图像。
据我所知，我的语法是正确的，但图像永远不会内联加载（但是它们已成功附加）。
From: email@example.com
Reply-To: email@example.com
MIME-Version: 1.0
Content-type: multipart/mixed;boundary="d0f4ad49cc20d19bf96d4adf9322d567"
Message-Id: <20150421165500.0A5488021B@server>
Date: Tue, 21 Apr 2015 12:54:59 -0400 (EDT)
--d0f4ad49cc20d19bf96d4adf9322d567
Content-type: text/html; charset=utf-8
Content-transfer-encoding: 8bit
<html>
Html message goes here, followed by email.<br/>
<img src="cid:mylogo" />
</html>
--d0f4ad49cc20d19bf96d4adf9322d567
Content-type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet; name=excelsheet.xlsx
Content-Description: excelsheet.xlsx
Content-Disposition: attachment;
filename="excelsheet.xlsx"; size=24712;
Content-transfer-encoding:base64
[base64 encoded string goes here.]
--b19e863e2cf66b40db1d138b7009010c
Content-Type: image/jpeg;
name="mylogo.jpg"
Content-transfer-encoding:base64
Content-ID: <mylogo>
Content-Disposition: inline;
filename="mylogo.jpg"; size=7579;
[base64 encoded string goes here.]
--b19e863e2cf66b40db1d138b7009010c--
有人能看出图像无法按预期嵌入的明显原因吗？
编辑
请注意，并非所有电子邮件客户端都存在这种行为。到目前为止只在 Thunderbird 中提到过。
我注意到两个问题：
MIME 边界不一致。对于第一个附件，它是 d0f4ad49cc20d19bf96d4adf9322d567，然后使用 b19e863e2cf66b40db1d138b7009010c。因此，从技术上讲，第二个附件是第一个附件的“一部分”。
如果您将所有 b19e863e2cf66b40db1d138b7009010c 替换为 d0f4ad49cc20d19bf96d4adf9322d567 Thunderbird 会正确识别图像附件。
使用 multipart/related 而不是 multipart/mixed。 （参见 RFC2387）
A multipart/related is used to indicate that each message part is a component of an aggregate whole. It is for compound objects consisting of several inter-related components - proper display cannot be achieved by individually displaying the constituent parts. The message consists of a root part (by default, the first) which reference other parts inline, which may in turn reference other parts. Message parts are commonly referenced by the "Content-ID" part header. (see Wikipedia entry for MIME multipart/related)
我在 PHP 应用程序中生成电子邮件，该应用程序将多个文件附加到 HTML 电子邮件。有些文件是 Excel 电子表格，有些文件是需要嵌入到 HTML 中的公司徽标，因此它们默认加载时使用 Content-ID 和 cid 标识符来引用附加图像。
据我所知，我的语法是正确的，但图像永远不会内联加载（但是它们已成功附加）。
From: email@example.com
Reply-To: email@example.com
MIME-Version: 1.0
Content-type: multipart/mixed;boundary="d0f4ad49cc20d19bf96d4adf9322d567"
Message-Id: <20150421165500.0A5488021B@server>
Date: Tue, 21 Apr 2015 12:54:59 -0400 (EDT)
--d0f4ad49cc20d19bf96d4adf9322d567
Content-type: text/html; charset=utf-8
Content-transfer-encoding: 8bit
<html>
Html message goes here, followed by email.<br/>
<img src="cid:mylogo" />
</html>
--d0f4ad49cc20d19bf96d4adf9322d567
Content-type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet; name=excelsheet.xlsx
Content-Description: excelsheet.xlsx
Content-Disposition: attachment;
filename="excelsheet.xlsx"; size=24712;
Content-transfer-encoding:base64
[base64 encoded string goes here.]
--b19e863e2cf66b40db1d138b7009010c
Content-Type: image/jpeg;
name="mylogo.jpg"
Content-transfer-encoding:base64
Content-ID: <mylogo>
Content-Disposition: inline;
filename="mylogo.jpg"; size=7579;
[base64 encoded string goes here.]
--b19e863e2cf66b40db1d138b7009010c--
有人能看出图像无法按预期嵌入的明显原因吗？
编辑
请注意，并非所有电子邮件客户端都存在这种行为。到目前为止只在 Thunderbird 中提到过。
我注意到两个问题：
MIME 边界不一致。对于第一个附件，它是
d0f4ad49cc20d19bf96d4adf9322d567，然后使用b19e863e2cf66b40db1d138b7009010c。因此，从技术上讲，第二个附件是第一个附件的“一部分”。如果您将所有
b19e863e2cf66b40db1d138b7009010c替换为d0f4ad49cc20d19bf96d4adf9322d567Thunderbird 会正确识别图像附件。使用
multipart/related而不是multipart/mixed。 （参见 RFC2387）A multipart/related is used to indicate that each message part is a component of an aggregate whole. It is for compound objects consisting of several inter-related components - proper display cannot be achieved by individually displaying the constituent parts. The message consists of a root part (by default, the first) which reference other parts inline, which may in turn reference other parts. Message parts are commonly referenced by the "Content-ID" part header. (see Wikipedia entry for MIME multipart/related)