You can use the following settings to ensure that Dovecot and Postfix use a modern TLS version:

For Dovecot:

1. Open the file /etc/dovecot/conf.d/10-ssl.conf (Debian).
2. Uncomment the line starting with ssl_min_protocol and set it to ssl_min_protocol = TLSv1.2.

For Postfix:

1. Open the file /etc/postfix/main.cf (Debian).
2. Add the following directive: smtpd_tls_mandatory_protocols = !SSLv2,!SSLv3,!TLSv1,!TLSv1.1.

Finally, reload Postfix with systemctl reload postfix and restart Dovecot with systemctl restart dovecot.