For errors like the one @jmoudy is reporting (No module named 'packaging'), you can try:
sudo rm -rf /usr/local/lib/python3.4/dist-packages/{pkg_resources,setuptools}*
apt-get install --reinstall python3-setuptools python3-pip python3-pkg-resources
And then run the Mail-in-a-Box setup again.
For errors like the one @netoperatorwibby is reporting (cffi library '_openssl' has no function), try:
sudo rm -rf /usr/local/lib/python3.4/dist-packages/cryptography*
And then run the Mail-in-a-Box setup again. See this earlier post about that problem.