Many thanks for the further observations and for the sample message.
Be advised, the following is my opinion and doesn't reflect any attempt to force my vision or interpretation on to you or others.
A great deal of the problem is to do with the complicated construction of the email message and the image source. It is important the images (jpg, bmp, png) are served from a valid secure source (https) and that the construction of the email doesn't include any tactics to hide content (hidden CSS etc). If it does then doogiePIM will tend not to render that content. You get this with some advertising type email messages.
Also consider the number of remote images in the message. The sample you sent to me contained over 50 images from many different sources that were used in constructing a jigsaw of a single page. This may be acceptable for displaying on a public web page, albeit highly uneconomical, but not for an email message that is used for private communication. As doogiePIM is attempting to concentrate on securing your data and privacy I wouldn't like to let through an email message that lacks consideration for bandwidth, privacy and security.
If you switch to plain text only, you should be able to understand the message without CSS styles and remote images.
Finally, consider the effect of remote images. Upon downloading and showing an image in a message, you are telling someone else, (the server the image is stored on), you've opened the email message. Again, acceptable for public pages but not for personal correspondence.
I appreciate doogiePIM has flaws and needs be enhanced further with better rendering of messages and my goal is to realise this as soon as I'm able to find ways of doing this without compromising our privacy.
I'm very happy you've considered doogiePIM and hope you continue to use the features and sections sans Messages.