Text encoding in Mozilla Thunderbird

Depending on your e-mail service it is neccessary to set default encoding

If special characters (äöüßøé etc) in your messages look cryptic to the reader, you must adjust the Thunderbird settings. You will probably notice this when you regularly receive replies with these cryptic characters. My AOL account only seems to accept UTF-8 unicode characters for outgoing mail.
If you compose a mail you can set the encoding under options in the "write" window. But this is not permanent.
The default encoding for incoming and outgoing messages can be set in the main window under Tools - Options - Display - Fonts and Colours - Advanced (next to it, not the upper advanced tab!). Btw this is independent from the plain text option in Tools - Options - Composition - Send Options.
From another E-Mail service i use, both Western and UTF-8 were sent correctly.