I have tried to file E Mails with attached pictures into DTP Pro Office. The EMail is visible - headers, subject, etc but in some cases the pictures do not appear but usually there is a blank grid of various sizes where the pictures should be.
Some of the pictures were taken with an iPhone, others may not have been. Seems this problem is brand independent.
If you checked the option in DEVONthink Pro Office Preferences > Email - Download remote images in HTML messages, the images will always be present in the message captured to DEVONthink.
However, the default view of email uses Apple’s Quick Look, and images and attachments are not visible.
To make the images (and attachments) visible, click on the Text Alternative button in the navigation bar immediately above the pane in which the email message content is displayed. This will switch to a rich text view of the message.