Running kmail 5.2.3 in Mint 18 KDE. Migrated my messages from Mint 17.3 with some incident (the PIM settings exporter didn't bring the e-mails in, but copying the backup into the new kmail folder seemed to work).

However, none of the message headers are showing up in the preview window. There used to be options under View -> Headers, but now there is nothing in there.

I would attach a screen shot if I could figure out how to. Any help will be greatly appreciated. Thanks!

A little more info. Parts of the graphical elements for previous message headers seem to be sitting in /usr/share/libmessageviewer/pics. For example, a locate shows this (partial listing):

/usr/share/libmessageviewer/pics/enterprise_bottom.png
/usr/share/libmessageviewer/pics/enterprise_bottom_left.png
/usr/share/libmessageviewer/pics/enterprise_bottom_right.png
/usr/share/libmessageviewer/pics/enterprise_icon.png
/usr/share/libmessageviewer/pics/enterprise_left.png
/usr/share/libmessageviewer/pics/enterprise_right.png
/usr/share/libmessageviewer/pics/enterprise_s_left.png
/usr/share/libmessageviewer/pics/enterprise_s_right.png
/usr/share/libmessageviewer/pics/enterprise_sbar.png
/usr/share/libmessageviewer/pics/enterprise_sp_right.png
/usr/share/libmessageviewer/pics/enterprise_sw.png
/usr/share/libmessageviewer/pics/enterprise_top.png
/usr/share/libmessageviewer/pics/enterprise_top_left.png
/usr/share/libmessageviewer/pics/enterprise_top_right.png
/usr/share/libmessageviewer/pics/enterprise_w.png

I don't have a package called libmessageviewer (none seems to be in the repository), but an apt search shows this:

mannex@Aculeus:~$ apt search messageviewer
p libkf5messageviewer-dev - KDE PIM messaging library, message viewer
p libkf5messageviewer-dev:i386 - KDE PIM messaging library, message viewer
i libkf5messageviewer5 - KDE PIM messaging library, message viewer
p libkf5messageviewer5:i386 - KDE PIM messaging library, message viewer

Which seems to indicate that the libkf5messageviewer5 is installed. Is there something missing from the headers that didn't get installed? Is anyone else having this issue?

I'm sorry to say that, due to another issue as well (the missing separate widgets on each desktop issue), I'm leaving KDE. Thus, this will no longer be an issue. Sorry to see it go, but it seems that the previous version was the best, and now they have opted for losing popular features.

You were a little too fast: all you needed was to check if you had "kdepim-addons" installed. As another user reported this a few weeks ago, and they were also running MInt, this tells me it is a Mint packaging problem (some required packages are not pulled in).

Ah, thanks for that. Not too fast, though, as there were lots of other issues with the upgrade. I really don't like the fact that you can't have separate wallpapers on different desktops without resorting to the Activities kludge. So, I've gone back to the previous version whilst I check out Cinnamon and some other desktops. Sad that KDE offers by far the best option in my opinion, but it's just simply idiotic to offer a desktop cube when all sides of the cube have to look the same. Makes no sense. And if that's the kind of thinking driving newer releases, I need to look elsewhere.

But thank you for that reply! Should the issues be addressed in a future release, then this will come in handy, no doubt!