Update to latest upstream version, see following page for changes: https://www.mozilla.org/en-US/thunderbird/38.1.0/releasenotes/
This update also should fixed problems with thunderbird-lightning-gdata package. Rebase to Thunderbird 38. By this release thunderbird-lightning (calendar) package has become obsolete, because it is a part of Thunderbird 38 package now.
For changes see: https://www.mozilla.org/en-US/thunderbird/38.0.1/releasenotes/
Updates may require up to 24 hours to propagate to mirrors. If the following command doesn't work, please retry later:
sudo dnf upgrade --refresh --advisory=FEDORA-2015-11502
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