Seems as we are similar refugees
I just tried your solution and - as expected - it is working.
But to simplify stuff, I didn't create a wrapper-script, /usr/bin/thunderbird is already a wrapper script. I just added the

after line 38.
I also had a look at the Debian issue (https://bugs.debian.org/cgi-bin/bugrepo … bug=784289). The reporter closed the issue because after the upgrade to GnuPG 2.1.4 it is working again. In ascii, there is GnuPG 2.1.18 available, perhaps this solved the issue?

Thanks for your answers. I do have everything installed using .deb-Packages (I try to install nearly everything from packages because my hope is, that upgrades are as smooth as possible )
Before I made an upgrade on an additional machine, I had a quick look and realized, enigmail 1.8.2 was installed as "amd64" and the amd64 package is still on 1.8.2 in debian. Enigmail 1.9.8 is only available as "all" package and this might explain why it was not upgraded - though in my opinion, there should be at least a transitional package enigmail-amd64 to automate the process. But this seems as a Debian issue to me.
Thank you for your hint about the problem of encrypting messages. Until now, I just tried to decrypt messages and as soon as I got this running, I thought to have solved the issue. I can't verify right now, but I will as soon as possible.
I'm not sure staying at TB 45.8 is a good solution, since the upgrade is marked as a security-upgrade.
Did you have a look at https://enigmail.net/index.php/en/faq?view=topic&id=14 - it did not work for me, but perhaps it helps you

Thanks for the great news. I followed the instructions (if someone else tries to follow: the package is named "xfce4-power-manager") and I have the XFCE Power Manager in my Preferences Menu available. As you have mentioned: the "close lid" stuff is unresolved (I already thought about a cron job checking the lid status every minute and sending the dbus if it is closed )

I wasn't aware of this fact - I am using MATE nearly since it is available and never had the problem.

I also have the issue with the battery icon, but I resolved this by hiding the icon from power-management and putting "Battery Charge Monitor" instead. Does MATE 1.14 solve only the battery issue or also the Suspend/Hibernate issue?
If not: does someone know a workaround? I'm using Linux on all my machines and they are in use by the whole family. They won't care about technical stuff, they just close the lid and expect the system to suspend. On the main laptop I still have Debian jessie installed (suspend working there) and not even having a workaround is a showstopper for migrating to Devuan

mate-about pops up a window with:

MATE Desktop Environment 1.8.1
MATE is a Free, usable, stable, accessible desktop environment for the Unix-like family of operating systems.
Copyright © 1997-2011 GNOME developers
Copyright © 2011 Perberos
Copyright © 2012-2014 MATE developers
http://www.mate-desktop.org/

And a "Credits" and a "Close" button.
I checked the installed version:

$ apt-show-versions mate-desktop
mate-desktop:amd64/jessie 1.8.1+dfsg1-3+deb8u1 uptodate