你需要像这样声明你的图片:

You need to declare your images like this :

<img src="cid:unique-name-or-id" />

将图像加载为 MimeBodyPart，并将唯一名称或 ID 与 MimeBodyPart 的文件名匹配.

Load images as MimeBodyPart and match the unique-name-or-id with the FileName of the MimeBodyPart.