Debian – Getting error TLS not available when connect via StartTLS

I am trying to configure TLS on my mail server (postfix+dovecot on debian).

But whenever I try to send via StartTLS, I've got this error message

telnet localhost 25
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 Vulcan0.hijackedbrain.com ESMTP Postfix (Debian/GNU)
starttls
454 4.7.0 TLS not available due to local problem

Here is my main.cf postfix, especially TLS parameters

# TLS parameters
smtpd_tls_cert_file=/etc/postfix/myCert.cert
smtpd_tls_key_file=/etc/postfix/RSA.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_tls_security_level = encrypt
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom
smtp_tls_loglevel = 3
smtpd_tls_auth_only = yes

I checked the certificate using openssl verify. It seems OK.

Any help would be appreciated. Thanks