How do I back up Thunderbird emails?
I currently use 10.04LTS and want to upgrade to 12.04LTS. How do I get my inbox and sent messages backed up so that I can re-open them in the new version?
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
The best way is to backup the Thunderbird profile.
Open your Homoe directory, Press Ctrl+H to show hidden files and folder, look for ".thunderbird" folder and save it somewhere. After upgrade just put it back there.