http://lpoaj76nfopd5lpinbskyqtroppamrzhhay3g4vvjm75st6ger34lbyd.onion/posts/2020/08/email-sucks.html
It does not offer encryption of most metadata, such as sender and receiver, like email, it is held back by backwards compatibility, and it has tons of other issues, as described in this latacora post , for example.