Question: Is the Sunbird logo available under a MPL/GPL/LGPL license?
Answer: Not at this time, and it probably never will be.
The Sunbird logo and the word mark "Mozilla Sunbird" are trademarks of the Mozilla Foundation.
They are used to identify products of the Mozilla Foundation, and may not be used for to identity derivitive works
produced outside of the authority of the Mozilla Foundation. Since it is a trademark, the logo's use is restricted.
Refer to these Mozilla pages regarding Trademarks:
Mozilla Trademark Policy
Mozilla Trademark Policy for Localization Projects
The Sunbird logo is a copyrighted work which has been assigned to the Mozilla Foundation by Mark L. Carson.
The logo is also licensed to the Mozilla Foundation for use as a Trademark.