code: @Override
      public void accept(Postcard postcard) {
          readyPostcardFirst(postcard);
          checkPostcardFirst(postcard);
          if (postcard.isForcedlyDirect()) { // should ignore body file
              assertPlainBodyExistsForDirectBody(postcard);
              postcard.getBodyFile().ifPresent(bodyFile -> { // but wants logging
                  officeManagedLogging(postcard, bodyFile, prepareReceiverLocale(postcard));
              });
              return;
          }
          postcard.getBodyFile().ifPresent(bodyFile -> {
              if (postcard.getHtmlBody().isPresent()) {
                  String msg = "Cannot use direct HTML body when body file is specified: " + postcard;
                  throw new SMailIllegalStateException(msg);
              }
              final boolean filesystem = postcard.isFromFilesystem();
              final OptionalThing<Locale> receiverLocale = prepareReceiverLocale(postcard);
              final OptionalThing<Object> dynamicData = prepareDynamicData(postcard, bodyFile, filesystem, receiverLocale);
              dynamicData.ifPresent(data -> acceptDynamicProperty(postcard, bodyFile, filesystem, receiverLocale, data));
              officeManagedLogging(postcard, bodyFile, receiverLocale);
              final String plainText = readText(postcard, bodyFile, false, filesystem, receiverLocale, dynamicData);
              analyzeBodyMeta(postcard, bodyFile, plainText);
              final DirectBodyOption option = postcard.useDirectBody(plainText);
              if (postcard.isAlsoHtmlFile()) {
                  final String htmlFilePath = deriveHtmlFilePath(bodyFile);
                  final String readHtml = readText(postcard, htmlFilePath, true, filesystem, receiverLocale, dynamicData);
                  verifyMailHtmlTemplateTextFormat(htmlFilePath, readHtml);
                  option.alsoDirectHtml(readHtml);
              }
              // no check about unneeded HTML template file because of runtime performance
              // DBFlute generator checks it instead
          }).orElse(() -> { /* direct body, check only here */
              assertPlainBodyExistsForDirectBody(postcard);
          });
          if (!postcard.getFrom().isPresent()) { // is moved from office check of postcard for dynamic property
              throwMailFromAddressNotFoundException(postcard);
          }
      }
docs: =============