As mentioned in https://libreplanet.org/wiki/List_of_software_that_does_not_respect_the_Free_System_Distribution_Guidelines
Description: Email client
Homepage: http://www.mozillamessaging.com/thunderbird/
Problem: Recommends non-free software (extensions) and non-free searchplugins.
Recommended Fix: Change link to point to GNUzilla's list of free addons and apply searchplugins-libre.patch to remove non-free search plugins replacing them with duckduckgo and identi.ca.
References: Parabola GNU/Linux - Bugs: bug #81, thunderbird-libre has non-free searchplugins (Freedom issue #81)
Copyright file: thunderbird copyright file
(Source) package name(s): icedove, thunderbird
@todd should we maybe rebrand it as well?
P.S. we need to check PureOS against that list.