MarsSeed [1] filed a deletion request for thunderbird-tbsync-beta [2]: Long-abandoned and orphaned package (last updated in 2018). There is a stable (albeit also orphaned) AUR package for this. Also, this Thunderbird addon project is still alive and current, and the latest version of the module is available from addons.thunderbird.net. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/thunderbird-tbsync-beta/