certtool works fine:
certtool --load-ca-certificate=ca.pem --verify --infile user-cert.pem
...
Chain verification output: Verified. The certificate is trusted.
But exim selects EC/ECDSA and fails:
13833 host in tls_try_verify_hosts? yes (matched "*")
13833 TLS: a client certificate will be requested but not required.
13833 SMTP>> 220 TLS go ahead
13833 GnuTLS<3>: ASSERT: ../../lib/buffers.c[get_last_packet]:1171
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/server_name.c[gnutls_server_name_get]:240
13833 TLS: no SNI presented in handshake.
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/psk_ke_modes.c[psk_ke_modes_recv_params]:136
13833 GnuTLS<2>: checking 13.02 (GNUTLS_AES_256_GCM_SHA384) for
compatibility
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/server_name.c[gnutls_server_name_get]:240
13833 GnuTLS<1>: The hash size used in signature (32) is less than the
expected (48)
13833 GnuTLS<3>: ASSERT: ../../lib/pubkey.c[pubkey_supports_sig]:1905
13833 GnuTLS<2>: Selected (EC/ECDSA) cert based on ciphersuite 13.2:
GNUTLS_AES_256_GCM_SHA384
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/key_share.c[key_share_recv_params]:576
13833 GnuTLS<3>: ASSERT: ../../lib/hello_ext.c[hello_ext_parse]:274
13833 GnuTLS<3>: ASSERT: ../../lib/extv.c[_gnutls_extv_parse]:69
13833 GnuTLS<3>: ASSERT:
../../lib/hello_ext.c[_gnutls_parse_hello_extensions]:307
13833 GnuTLS<3>: ASSERT: ../../lib/handshake.c[read_client_hello]:825
13833 GnuTLS<3>: ASSERT: ../../lib/handshake.c[_gnutls_recv_handshake]:1552
13833 GnuTLS<3>: ASSERT: ../../lib/buffers.c[get_last_packet]:1171
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/server_name.c[gnutls_server_name_get]:240
13833 TLS: no SNI presented in handshake.
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/psk_ke_modes.c[psk_ke_modes_recv_params]:136
13833 GnuTLS<2>: checking 13.02 (GNUTLS_AES_256_GCM_SHA384) for
compatibility
13833 GnuTLS<3>: ASSERT:
../../../lib/ext/server_name.c[gnutls_server_name_get]:240
13833 GnuTLS<1>: The hash size used in signature (32) is less than the
expected (48)
13833 GnuTLS<3>: ASSERT: ../../lib/pubkey.c[pubkey_supports_sig]:1905
13833 GnuTLS<2>: Selected (EC/ECDSA) cert based on ciphersuite 13.2:
GNUTLS_AES_256_GCM_SHA384
13833 GnuTLS<2>: EXT[0x55a80c132460]: server generated SECP521R1 shared key
13833 GnuTLS<1>: The hash size used in signature (32) is less than the
expected (48)
13833 GnuTLS<3>: ASSERT: ../../lib/pubkey.c[pubkey_supports_sig]:1905
13833 GnuTLS<3>: ASSERT: ../../../lib/nettle/mpi.c[wrap_nettle_mpi_print]:60
13833 GnuTLS<3>: ASSERT: ../../../lib/nettle/mpi.c[wrap_nettle_mpi_print]:60
13833 GnuTLS<3>: ASSERT: ../../lib/constate.c[_gnutls_epoch_get]:923
13833 GnuTLS<3>: ASSERT: ../../lib/buffers.c[get_last_packet]:1171
13833 GnuTLS<3>: ASSERT: ../../lib/tls13/certificate.c[parse_cert_list]:406
13833 GnuTLS<3>: ASSERT:
../../lib/tls13/certificate.c[_gnutls13_recv_certificate]:110
13833 GnuTLS<3>: ASSERT: ../../lib/buffers.c[get_last_packet]:1171
13833 GnuTLS<3>: ASSERT:
../../lib/tls13/session_ticket.c[_gnutls13_send_session_ticket]:284
13833 gnutls_handshake was successful
13833 TLS: checking peer certificate
13833 TLS: no certificate from peer ((nil) & 0)
13833 The certificate is NOT trusted. The certificate chain is revoked.
The certificate doesn't match the local copy (TOFU). The revocation or
OCSP data are old and have been superseded. The revocation or OCSP data
are issued with a future date. The certificate issuer is not a CA. The
certificate chain does not match the intended purpose. The certificate
chain uses expired certificate. The received OCSP status response is
invalid. The certificate contains an unknown critical extension.
13833 TLS certificate verification failed (certificate revoked):
peerdn="<unset>"
13833 TLS verify failure overridden (host in tls_try_verify_hosts)
13833 cipher: TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256
