Correct Mail Translate does not collect, store or transmit any personal data by itself. When you choose a menu entry, the selected text (or the text of the chosen message) is placed into a link to https://translate.google.com/ and opened in your default web browser. The text is thereby sent to Google; Google's privacy policy applies (https://policies.google.com/privacy). If the text is too long for a link, it is only copied to your local clipboard, and the Google Translate page is opened without text. The only data stored by the add-on are your settings (target language, line joining), kept locally in Thunderbird.