debugging "(gnutls_handshake): No supported cipher suites have been found"

Hello,

looking at my mail server logs I have found 

2021-02-20 12:13:53 TLS error on connection from [...] (gnutls_handshake): No supported cipher suites have been found.

for incoming connections, outgoing connections to the same host succeed
with X=TLS1.2:ECDHE_SECP256R1__RSA_SHA256__AES_256_GCM:256

My host is running Debian/stable (gnutls 3.6.7), I have also tried with
gnutls 3.6.15 or with priorities NORMAL:-VERS-TLS1.3 or NORMAL:%COMPAT.

cu Andreas
-- 
`What a good friend you are to him, Dr. Maturin. His other friends are
so grateful to you.'
`I sew his ears on from time to time, sure'