Comment 5 for bug 1683516

Working 16.04 MATE solution is below.
In brief:
1. install indicator stuff (libindicate-gtk3, libindicate5, python-indicate, python-gnomekeyring, python-notify).
2. get old packages from Ubuntu 12.04 (python-support, libindicator-messages-status-provider1, indicator-messages, indicator-messages-gtk2).
3. test with Popper (https://launchpad.net/~ralf.hersel/+archive/ubuntu/rhersel-ppa).

### for 16.04 MATE
sudo apt-get install libindicate-gtk3 libindicate5 python-indicate python-gnomekeyring python-notify

cd ~/Downloads
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/python-support/python-support_1.0.14ubuntu2_all.deb
sudo dpkg -i python-support_1.0.14ubuntu2_all.deb

wget http://ppa.launchpad.net/ralf.hersel/rhersel-ppa/ubuntu/pool/main/p/popper/popper_0.31.3-0ubuntu1_all.deb
sudo dpkg -i popper_0.31.3-0ubuntu1_all.deb

wget http://archive.ubuntu.com/ubuntu/pool/main/i/indicator-messages/libindicator-messages-status-provider1_0.6.0-0ubuntu2_i386.deb
sudo dpkg -i libindicator-messages-status-provider1_0.6.0-0ubuntu2_i386.deb

wget http://archive.ubuntu.com/ubuntu/pool/main/i/indicator-messages/indicator-messages_0.6.0-0ubuntu2_i386.deb
sudo dpkg -i indicator-messages_0.6.0-0ubuntu2_i386.deb

wget http://archive.ubuntu.com/ubuntu/pool/universe/i/indicator-messages/indicator-messages-gtk2_0.6.0-0ubuntu2_i386.deb
sudo dpkg -i indicator-messages-gtk2_0.6.0-0ubuntu2_i386.deb

Launch mate-tweak: Panel (Interface) -> Enable indicators.

Go to Applications -> Internet -> Popper (or launch popper-config).
Popper will work, check and indicate new e-mails as on Ubuntu 12.04.5 LTS.

For 16.04 do not forget to set packages pin:
cat <<EOF | sudo tee /etc/apt/preferences.d/pin-indicators
Package: indicator-messages
Pin: version 0.6.0-0ubuntu2
Pin-Priority: 1337

Package: indicator-messages-gtk2
Pin: version 0.6.0-0ubuntu2
Pin-Priority: 1337

Package: libindicator-messages-status-provider1
Pin: version 0.6.0-0ubuntu2
Pin-Priority: 1337

Package: popper
Pin: version 0.31.3-0ubuntu1
Pin-Priority: 1337

Package: python-support
Pin: version 1.0.14ubuntu2
Pin-Priority: 1337

EOF