I checked the problem with displaying inline images in HTML (MIME) mails also in 8.5 Beta 1 and I can confirm that it is the same as in LN 8.0.1.
The problem is related to the preference option “Disable embedded browser for MIME mail”.
If this option is selected then the mail is displayed (including inline images) by the LN client itself with all old problems in rendering.
If the option is not selected then the embedded browser is used instead but then inline images are not displayed at all.
It would be nice to have the possibility to use the embedded browser for MIME mails because of its rendering possibilities.
Milos Lapis
MLC