Some reason the newest Thunderbird is not available in Mint 18 and Ubuntu 16.04, so the solution is to install Ubuntuzilla’s version.

https://sourceforge.net/p/ubuntuzilla/wiki/Main_Page/#installation

echo -e "\ndeb http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all main" | sudo tee -a /etc/apt/sources.list > /dev/null

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 2667CA5C

sudo apt-get update

sudo apt-get install thunderbird-mozilla-build