Comment 6 for bug 1104124

Ok, i solved the issue going to Edit > Preferences > Display: under Fonts > Advanced and there was Western ISO .. and UTF-8 encodings in outgoing and incoming. The issue still in the sense that you actually can set up UTF-8 encoding when composing messages and when hit send, Thunderbird changes the encoding to Western and the spanish tildes go bananas and the PGP sign gives a different hash that the one that was calculated in UTF-8 ebcoding. This is still an issue because when you change encoding for a particular message, the above setting overrides it and messes up with the PGP sign validity.

Regards,