added anti-blocking inline images in "Mass Mailer Attack"

[s0i37]

I noticed, that all images in emails has banned. For example:

<img src="http://external.resource/image.png">
or
<img src="data:image/gif;base64,aaaabbbbccccddddeeee=">

But if we send image as:

...
Content-ID: <image1.png>
...

We will can to include one in html like this:

...
<img src="cid:image1.png">
...

This approach won't block. And we will see all images in our email.
In my opinion, an image is main part of social injection.