NodeJS中AWS SES多附件MIME邮件问题：仅首个附件生效

我正在使用AWS SES发送带附件的邮件，由于sendEmail函数不支持发送附件，因此采用SES的sendRawEmail函数。为发送原始邮件，我将邮件转换为如下MIME文本，包含两个转成base64的图片附件、正文及若干邮件头：

From: from@test.com
To: to@test.com
Cc: 
Bcc: 
Subject: Test from Lambda
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="----=_Part2904462804807624"


------=_Part2904462804807624
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit


Hello world


------=_Part2904462804807624
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 7bit


<h1>Hello</h1><p>world</p>


------=_Part2904462804807624
Content-Type: image/jpeg; name="sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg"
Content-Description: sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg
Content-Disposition: attachment;filename="sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg";
Content-Transfer-Encoding: base64


/9j/4AAQSkZJRgABAQAAAQABAAD/4gIcSUNDX1BST0ZJTEUAAQEAAAIMbGNtcwIQAABtbnRyUkdCIFhZWiAH3AABABkAAwApADlhY3NwQVBQTAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA9tYAAQAAAADTLWxjbXMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAApkZXNjAAAA/
.....................................
.....................................
.....................................
MOO3FwVjiwfsg1fcci0NRnULhYioZ2KOJRlg33mWBSNrslR+COggrOdzIshEqj4ghEN3WU6jhDlg8zDHGYoRsMNKcauLzWjjzBY26eC5ZFlpeI0fITV8EdMstRZcj4mTDEpYYeTuUa1+yBUdHBcs8rdahAOUiCgJLUZEn/9k=


------=_Part2904462804807624--
Content-Type: image/jpeg; name="image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg"
Content-Description: image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg
Content-Disposition: attachment;filename="image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg";
Content-Transfer-Encoding: base64


/9j/4AAQSkZJRgABAgAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRofHh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/2wBDAQkJCQwLDBgNDRgyIRwhMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjL/wAARCALQBQADASIAAhEBAxEB/
.....................................
.....................................
.....................................
ojzPGee6OP61rQa14b06zmutOtLmw1KJSsSTpvILcZV+gx7it/wJaNeeEbqGWK2uIgSttHKoIRwD8p7gZx/Sli023sNae2j0mzS9njKkGcm3kTA3ADdlST6qc150q1HmdNrbs/0Dof/2Q==


------=_Part2904462804807624--
------=_Part2904462804807624--

邮件发送后仅第一个附件能被成功添加，第二个附件无法显示（截图如下），单独测试第二个附件时功能正常，请问该MIME文本存在什么问题？

问题分析与解决方案 #

核心问题 #

你的MIME文本存在两处致命错误：

• 提前闭合了MIME边界：第一个附件结束后，你使用了------=_Part2904462804807624--（末尾带两个连字符的闭合标记），这会直接终止整个multipart/alternative容器，后续的第二个附件被视为边界外的无效内容，无法被邮件客户端解析。
• 冗余的闭合标记：文本末尾重复出现多次------=_Part2904462804807624--，属于无效内容，会干扰邮件解析。

修正后的MIME结构 #

调整边界使用规则，确保所有内容（正文、两个附件）都在容器内，仅在最后使用一次闭合标记：

From: from@test.com
To: to@test.com
Cc: 
Bcc: 
Subject: Test from Lambda
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="----=_Part2904462804807624"


------=_Part2904462804807624
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit


Hello world


------=_Part2904462804807624
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 7bit


<h1>Hello</h1><p>world</p>


------=_Part2904462804807624
Content-Type: image/jpeg; name="sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg"
Content-Description: sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg
Content-Disposition: attachment;filename="sea-surface-turquoise-blue-color-background-some-reflections-calm-crystal-clear-water-small-ripples-sea-surface-turquoise-221064440.jpg";
Content-Transfer-Encoding: base64


/9j/4AAQSkZJRgABAQAAAQABAAD/4gIcSUNDX1BST0ZJTEUAAQEAAAIMbGNtcwIQAABtbnRyUkdCIFhZWiAH3AABABkAAwApADlhY3NwQVBQTAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA9tYAAQAAAADTLWxjbXMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAApkZXNjAAAA/
.....................................
MOO3FwVjiwfsg1fcci0NRnULhYioZ2KOJRlg33mWBSNrslR+COggrOdzIshEqj4ghEN3WU6jhDlg8zDHGYoRsMNKcauLzWjjzBY26eC5ZFlpeI0fITV8EdMstRZcj4mTDEpYYeTuUa1+yBUdHBcs8rdahAOUiCgJLUZEn/9k=


------=_Part2904462804807624
Content-Type: image/jpeg; name="image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg"
Content-Description: image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg
Content-Disposition: attachment;filename="image.desktop.size-xl.sme-greenoption-xl1280x720.jpeg";
Content-Transfer-Encoding: base64


/9j/4AAQSkZJRgABAgAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRofHh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/2wBDAQkJCQwLDBgNDRgyIRwhMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjIyMjL/wAARCALQBQADASIAAhEBAxEB/
.....................................
ojzPGee6OP61rQa14b06zmutOtLmw1KJSsSTpvILcZV+gx7it/wJaNeeEbqGWK2uIgSttHKoIRwD8p7gZx/Sli023sNae2j0mzS9njKkGcm3kTA3ADdlST6qc150q1HmdNrbs/0Dof/2Q==


------=_Part2904462804807624--

额外优化建议 #

multipart/alternative的设计初衷是提供同一内容的不同格式（比如纯文本和HTML正文），带附件的邮件更规范的做法是使用multipart/mixed作为顶层容器：

1. 顶层容器用multipart/mixed，设置对应的边界；
2. 内部嵌套一个multipart/alternative容器存放纯文本和HTML正文；
3. 在顶层容器下单独添加两个附件部分。

这种结构能更好兼容各类邮件客户端，避免解析异常。

内容的提问来源于stack exchange，提问作者Binara Medawatta