Icedove is a modified version of Thunderbird. It's common to have to modify
programs in order to fix freedom problems. Look at the Trisquel Helper
scripts and you can find all sorts of examples. Icedove does provide all four
freedoms. So, given that it's free software, there should be no issue with
people using it.
Does Trisquel actually provide an actual copy of Thunderbird? In looking
through my package manager it seems to provide a transitional thing for
people to request Thunderbird but actually get Icedove. Notice how the
package manager says "Note, selecting 'icedove' instead of 'thunderbird'":
apt install thunderbird
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'icedove' instead of 'thunderbird'
icedove is already the newest version
(1:52.7.0+build1-0ubuntu0.16.04.1+8.0trisquel1).
If you somehow find an actual copy of Thunderbird in Trisquel please report
it as a freedom issue so that it can be fixed.
