# this is a postfix config snippet, include me into /etc/postfix/main.cf
smtp_tls_protocols=!SSLv2,!SSLv3
smtp_tls_mandatory_protocols=!SSLv2,!SSLv3
smtpd_tls_protocols=!SSLv2,!SSLv3
smtpd_tls_mandatory_protocols=!SSLv2,!SSLv3
# for checking that service
openssl s_client -connect <hostname>:25 -starttls smtp -ssl3