Prior to the release of Thunderbird 13, the Dropbox feature which allowed users to attach large files from The Cloud (after uploading through Dropbox) had been removed [Bug 754993]. I recall early on there were some security concerns about this feature from business users. They had wanted the ability to disable this feature so that proprietary information couldn’t accidentally be placed on The Cloud. Now, it is being restored, as an add-on with a target milestone of Thunderbird 16 (due for release around October 9, 2012) [Bug 763471].
