send mails via ssl if possible

templates/main.cf.j2

@@ -40,6 +40,7 @@ smtpd_tls_key_file={{postfix_certificate_private_key_file}}
 smtpd_use_tls=yes
 smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
 smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
+smtp_tls_security_level = may
 
 
 ### transport configuration