Thunderbird 3.xx on Ubuntu

Note:  These steps only apply to Ubuntu versions prior to 10.04. Lucid Lynx already has Thunderbird 3 in its repositories.
 
Thunderbird 3 repository you add to your sources list to make Ubuntu automatically detect Thunderbird updates.

Testing this in Ubuntu 10.04 - from a fresh install.
1. From a terminal window, type:

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

2. Open Synaptic Package Manager and search for Thunderbird

3. Go and install.

This is a departure from my first approach from previous posts - that of downloading directly from the Thunderbird website and installing manually.

Taken from this Linux Mint post from user remoulder.