facing [ no shared cipher ] error with EC private keys. the client connecting to your instance has to support ecdsa
It does - Thunderbird 60.0b10 (64-bit)
[ security.ssl3.ecdhe_ecdsa_aes_256_gcm_sha384;true ]
It seems there is a difference between the private key (rsa vs. ecc -> SSL_CTX?) used for the certificate signing request and the signed certificate.
The csr created from a private key with [ openssl genpkey -algorithm RSA ] and signed by a CA with [ ecdhe_ecdsa ] works with no error.
But as stated in the initial message it does not work if the private key for the csr is generated with [ openssl ecparam -name brainpoolP512t1 -genkey ].
Can you show doveconf ssl_cipher_list?
Tried several variations, e.g. ALL, ALL:HIGH:MEDIUM:LOW and right now set to ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-AES256-GCM-SHA384 which is working fine when the csr was created from a private key with RSA algorithm but not if csr key is generated with an EC key.