Considering that the default value for smtpd_tls_mandatory_ciphers is medium it makes more sense to just remove the set_postfix_option "smtpd_tls_mandatory_ciphers = medium, high" line rather than replacing it with set_postfix_option "smtpd_tls_mandatory_ciphers = medium".
Thanks for preparing a debdiff.
Considering that the default value for smtpd_tls_ mandatory_ ciphers is medium it makes more sense to just remove the set_postfix_option "smtpd_ tls_mandatory_ ciphers = medium, high" line rather than replacing it with set_postfix_option "smtpd_ tls_mandatory_ ciphers = medium".