Is it possible to send embedded attachments?

It's true! To do this, you need to open the code editor (<> icon) and add an IMG tag with a cid. When cid is the parameter name of your attachment. For a static attachment, this is the name of the file with the extension.

For example, the attachment parameter name is "nice_cat", so the IMG tag will look like:

<img src="cid:nice_cat" alt="My Cat">

More information you can find on the embedded images guide.

Please note that only images can be embedded into the content.