How To File Enhancements
You can file a new enhancement request in Bugzilla, after searching through previous bugs to avoid duplication.
Be sure to select "Thunderbird" under product name and "Enhancement" as the severity.
also there is a Platform for new ideas and Requests at https://getsatisfaction.com/mozilla_messaging
The first step to triaging enhancements would be to search for duplicates to the bug. Resolve the bug as "DUPLICATE" if an earlier identical bug is found.
Developers will mark the bug as WONTFIX if there is no need for the enhancement and FIXED once the functionality is implemented.