Ndtyjky

I am trying to reply to a message using the gmail api, and I am confused in setting the In-Reply-To and references header, I am not sure what to set the value to and how to set the value. Please find my code below:

public static Message createMessageWithEmail(MimeMessage emailContent) throws Exception {

    ByteArrayOutputStream buffer = new ByteArrayOutputStream();

    emailContent.addRecipient(javax.mail.Message.RecipientType.TO, emailContent.getFrom()[0]);

    emailContent.setReplyTo(emailContent.getFrom());

    emailContent.setHeader("In-Reply-To", emailContent.getMessageID());

    emailContent.setHeader("References",emailContent.getMessageID());

    emailContent.setText("hi thank you");

    emailContent.writeTo(buffer);

    byte bytes = buffer.toByteArray();

    String encodedEmail = Base64.encodeBase64URLSafeString(bytes);

    Message message = new Message();

    message.setRaw(encodedEmail);

    return message;

  }









private static Message replyMessage(Gmail service, String userId, MimeMessage emailContent,Message messages) throws Exception {

    Message message = createMessageWithEmail(emailContent);

    message.setThreadId(messages.getThreadId());

    message.setId(messages.getId());

    message = service.users().messages().send(userId, message).execute();

    System.out.println("Message id: " + message.getId());

    System.out.println(message.toPrettyString());

    return message;

  }

Both of these headers come from RFC2822.

The parts relevant to your question are included on pages 23-24 (emphasis and formatting mine):

When creating a reply to a message, the "In-Reply-To:" and
"References:" fields of the resultant message are constructed as
follows:

• 
  The "In-Reply-To:" field will contain the contents of the "Message-ID:" field of the message to which this one is a reply (the "parent message"). If there is more than one parent message, then the "In-Reply-To:" field will contain the contents of all of the parents' "Message-ID:" fields. If there is no "Message-ID:" field in any of the parent messages, then the new message will have no "In-Reply-To:" field.


• 
  The "References:" field will contain the contents of the parent's "References:" field (if any) followed by the contents of the parent's "Message-ID:" field (if any). If the parent message does not contain a "References:" field but does have an "In-Reply-To:" field > containing a single message identifier, then the "References:" field will contain the contents of the parent's "In-Reply-To:" field followed by the contents of the parent's "Message-ID:" field (if any). If the parent has none of the "References:", "In-Reply-To:", or "Message-ID:" fields, then the new message will have no "References:" field.