How to forward attachments in a message

[runqi-zhao]

When I forward a message, the number of attachments in the message is dynamically obtained, how can I forward multiple attachments at once in the format of the sending message?

[paolobarbolini]

Assuming your starting point is something like

  let m = Message::builder()
      .from("NoBody <nobody@domain.tld>".parse()?)
      .to("Hei <hei@domain.tld>".parse()?)
      .subject("Something")
      // Rest of the headers...
      // and then:
      .multipart(MultiPart::alternative_plain_html(
          String::from("Plaintext version of the body"),
          String::from("Html version of the body"),
      ));

what you can do is change it to:

 let mut multipart = MultiPart::alternative_plain_html(
      String::from("Plaintext version of the body"),
      String::from("Html version of the body"),
  );

  for file in files_to_attach {
      let attachment = Attachment::new(file_name).body(bytes, content_type); // build `Attachment` here

      multipart = multipart.singlepart(attachment);
  }

  let m = Message::builder()
      .from("NoBody <nobody@domain.tld>".parse()?)
      .to("Hei <hei@domain.tld>".parse()?)
      .subject("Something")
      // Rest of the headers...
      // and then:
      .multipart(multipart);