Some HTML-containing messages that display correctly in version 3.11.1 do not display in 3.14.0. I think that version 3.13 also was affected.
Created attachment 1690 [details] html part that does not work but used to in older versions
check the comments on bug #3644, this is not a claws-mail bug. *** This bug has been marked as a duplicate of bug 3644 ***