@schroedingersdog @silmaril @thunderbird Maybe my question is where is your starting point: Did you start by moving your contacts to Nextcloud Contacts app, and then connect TBird to it? Or use Nextcloud to "store" your TBird sync? (I compare, I use Nextcloud for my Joplin note app to sync, where Nextcloud really only is a cloud for Joplin data, no native Nextclod app is involved). I am planning for my way back to TBird (from Apple mail).