diff --git a/templates/main.cf.j2 b/templates/main.cf.j2
index b38795aefdb16e3165421d71103397afce0d9f55..9a6c8e49ea6b6a8ff030459c4d174795788dc9a8 100644
--- a/templates/main.cf.j2
+++ b/templates/main.cf.j2
@@ -12,10 +12,10 @@ myorigin = {{ postfix__myorigin | default('$myhostname', true) }}
 {% endif %}
 
 smtpd_banner = {{ postfix__smtpd_banner }}
-biff = {{ postfix__biff }}
+biff = {{ 'yes' if postfix__biff else 'no' }}
 
 # appending .domain is the MUA's job.
-append_dot_mydomain = {{ postfix__append_dot_mydomain }}
+append_dot_mydomain = {{ 'yes' if postfix__append_dot_mydomain else 'no' }}
 
 # Uncomment the next line to generate "delayed mail" warnings
 {% if postfix__generate_delayed_mail_warnings %}
@@ -24,12 +24,12 @@ delay_warning_time = {{ postfix__delay_warning_time }}
 #delay_warning_time = {{ postfix__delay_warning_time }}
 {% endif %}
 
-readme_directory = {{ postfix__readme_directory }}
+readme_directory = {{ 'yes' if postfix__readme_directory else 'no' }}
 
 # TLS parameters
 smtpd_tls_cert_file = {{ postfix__smtpd_tls_cert_file }}
 smtpd_tls_key_file = {{ postfix__smtpd_tls_key_file }}
-smtpd_use_tls = {{ postfix__smtpd_use_tls }}
+smtpd_use_tls = {{ 'yes' if postfix__smtpd_use_tls else 'no' }}
 smtpd_tls_session_cache_database = {{ postfix__smtpd_tls_session_cache_database }}
 smtp_tls_session_cache_database = {{ postfix__smtp_tls_session_cache_database }}