not that we know off. As far as we know thunderbirds current extension model does not allow even an #autocrypt compliant plugin let alone all the rest that delta offers. #enigmail used to offer full autocrypt support but when thunderbird changed the plugin model and integrated openpgp into thunderbird they went back to the old idea of "users have to consciously manage their encryption keys" ... An unfortunate old tradition. We aim for modern usable security like signal delivers.

#chatmail servers are fully interoperate with classic e-mail servers. But end-to-end OpenPGP encryption is required (#autocrypt or #securejoin) and not all e-mail apps manage it in the automatic way that Delta Chat does it. Chatmail servers are minimal Postfix/Dovecot setups, fully FOSS, and anyone can run an chatmail server instance permission free without telling us.