21 Jun How do HTML messages work?

It is important that we are aware, that we cannot simply attach a HTML file containing a pile of images and click “send”. It is also not enough to only paste the HTML code into the email, because the broad majority of email clients will only show raw HTML code. It is necessary to send the HTML message from the server in a Multipart alternative MIME format. That means your email agent combines the HTML code and the “plain text” version into one message. In that way the message can also be seen by those recipients whose client doesn’t show the HTML version.

Image files in HTML messages
The main reason for sending email messages in HTML format is integrating images and photographs into messages. The correct way of managing images in HTML messages is that they are being hosted on a network server and then integrated it into the HTML code with the absolute path to the image.