Мой рабочий конфиг для CentOS 7, vsftpd 3.0.2 и OpenSSL 1.0.2k

ssl_enable=YES
allow_anon_ssl=NO
force_local_data_ssl=YES
force_local_logins_ssl=YES
ssl_tlsv1_1=YES
ssl_tlsv1_2=YES
ssl_tlsv1=NO
ssl_sslv2=NO
ssl_sslv3=NO
require_ssl_reuse=YES
ssl_ciphers=HIGH
rsa_cert_file=/etc/letsencrypt/live/rtfm.wiki/cert.pem
rsa_private_key_file=/etc/letsencrypt/live/rtfm.wiki/privkey.pem