I made working Thunderbird policy templates by taking the official Firefox templates from https://github.com/mozilla/policy-templates/ and renamed every occurrence of "Firefox" in "Thunderbird" and every "FF" in "TB".

This worked for the settings I needed but I didn't test all of them of course.

These templates are based on the Firefox templates v2.10 https://github.com/mozilla/policy-templates/releases/tag/v2.10