This is because thunderbird was recently updated to 3.0 in ubuntu but the enigmail package conflicts with thunderbirds of version greater than 2.0. Enigmail v 1.0 is needed to support thunderbird 3.0 according to the enigmail website.
This is because thunderbird was recently updated to 3.0 in ubuntu but the enigmail package conflicts with thunderbirds of version greater than 2.0. Enigmail v 1.0 is needed to support thunderbird 3.0 according to the enigmail website.