Thunderbird is a an MUA. If you've made the change from Internet explorer to the Firefox browser, you should give thunderbird a try. It also comes from Mozilla.
Remember your password
If you have to enter the password for your email account(s) every time you start Mozilla Thunderbird, you can open your prefs.js file on most UBOs
$ find ~ -name prefs.js | grep thunderbird
to find the file. open it, and modify the line that says:
and change false to true. Now start thunderbird again and you should be set.
I had an issue where thunderbird kept showing me 3 new messages in one folder, but when I clicked on that folder, there was nothing new. The next time I looked at thunderbird, it said 3 new messages in that folder again. What I did was right click on the folder, and chose both
Mark Folder Read Compact This Folder
Transition between Linux and Windows
You will want to copy the data from: (on Windows)
(If you do not see these folders in Windows explorer, you might need to change: Tools -> Folder options -> View -> Show hidden files and folders) to (on Linux)
(.thunderbird might also be .mozilla-thunderbird)
You can also follow these steps in reverse
I've used * above in place of xxxxxxx.default/, this is the directory you want to copy over. Before starting thunderbird on the other system, change profiles.ini from
IsRelative=1 to IsRelative=0
Path=Profiles/xxxxxx.default to Path=/home/you/.thunderbird/xxxxxx.default
Transition between Linux and OSX
scp -rp ~/.thunderbird on linux machine to ~/Library/Thunderbird on OSX.