How To Send A Reply With Gmail API

Question

I have two gmail accounts I created a thread consisting of five messages and retreived them with gmail gapi at this page https://developers.google.com/gmail/api/v1/reference/users/threads/get.

This is what I got:

As you can see, the ids don't match, although they identify the exact same letters. Why this happens, and how can i get the unified id?

P.S. The real reason I am doing this is that I need to send a reply to a message with gmail API, but to do that, you need to know the id of the message that you reply to. And if I reply to the message with id that I have ( not the message id that the receiver has ), it just sends a 'new' message.

How can I send replies with Gmail API?

Thank you in advance.

Solution 1

As the docs say, if you're trying to send a reply and want the email to thread, make sure that:

1. The Subject headers match
2. The References and In-Reply-To headers follow the RFC 2822 standard.

If you want to do this yourself, you could get the Subject, References and Message-ID-headers of the message you want to respond to:

Request:

userId = me
id = 14fd1c555a1352b7 // id of the message I want to respond to.
format = metadata
metadataHeaders = Subject,References,Message-ID

GET https://www.googleapis.com/gmail/v1/users/me/messages/14fd1c555a1352b7?format=metadata&metadataHeaders=Subject&metadataHeaders=References&metadataHeaders=Message-ID

Response:

{
 "id": "14fd1c555a1352b7",
 "threadId": "14fd1c52911f0f64",
 "labelIds": [
  "SENT",
  "INBOX",
  "IMPORTANT",
  "UNREAD"
 ],
 "snippet": "Next level dude 2015-09-15 18:10 GMT+02:00 Emil Tholin <[email protected]>: wow 2015-09-15 18:",
 "historyId": "575289",
 "internalDate": "1442333414000",
 "payload": {
  "mimeType": "multipart/alternative",
  "headers": [
   {
    "name": "In-Reply-To",
    "value": "<[e-mail]>"
   },
   {
    "name": "References",
    "value": "<CADsZLRxZDUGn4Frx80qe2_bE5H5bQhgcqGk=[e-mail]> <[e-mail]>"
   },
   {
    "name": "Message-ID", // This is the same for both users, as you were asking about.
    "value": "<CADsZLRwQWzLB-uq4_4G2E64NX9G6grn0cEeO0L=[e-mail]>"
   },
   {
    "name": "Subject",
    "value": "Re: Cool"
   }
  ]
 },
 "sizeEstimate": 1890
}

To follow the RFC 2822 standard we have added the Message-ID of the message we want to respond to to the References-header, separated with a space. The In-Reply-To-header also has the value of message we want to respond to. We also add Re: to our Subject-header to indicate that it is a response.

// Base64-encode the mail and make it URL-safe 
// (replace "+" with "-", replace "/" with "_", remove trailing "=")
var encodedResponse = btoa(
  "Content-Type: text/plain; charset=\"UTF-8\"\n" +
  "MIME-Version: 1.0\n" +
  "Content-Transfer-Encoding: 7bit\n" +
  "References: <CADsZLRxZDUGn4Frx80qe2_bE5H5bQhgcqGk=[e-mail]> <[e-mail]> <CADsZLRwQWzLB-uq4_4G2E64NX9G6grn0cEeO0L=[e-mail]>\n" +
  "In-Reply-To: <CADsZLRwQWzLB-uq4_4G2E64NX9G6grn0cEeO0L=[e-mail]>\n" +
  "Subject: Re:Cool\n" +
  "From: [email protected]\n" +
  "To: [email protected]\n\n" +

  "This is where the response text will go"
).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');

$.ajax({
  url: "https://www.googleapis.com/gmail/v1/users/me/messages/send?access_token=<USER_ACCESS_TOKEN>",
  method: "POST",
  contentType: "application/json",
  data: JSON.stringify({
    raw: encodedResponse
  })
});

As you can see, this is a pain in the backside to to manually. You could also just respond to the thread. This might not be enough for your use case however.

This way, you just have to supply the mail and the threadId, and make sure the Subject is the same, and Google will display it for you correctly.

// Base64-encode the mail and make it URL-safe 
// (replace "+" with "-", replace "/" with "_", remove trailing "=")
var encodedResponse = btoa(
  "Content-Type: text/plain; charset=\"UTF-8\"\n" +
  "MIME-Version: 1.0\n" +
  "Content-Transfer-Encoding: 7bit\n" +
  "Subject: Subject of the original mail\n" +
  "From: [email protected]\n" +
  "To: [email protected]\n\n" +

  "This is where the response text will go"
).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');

$.ajax({
  url: "https://www.googleapis.com/gmail/v1/users/me/messages/send?access_token=<USER_ACCESS_TOKEN>",
  method: "POST",
  contentType: "application/json",
  data: JSON.stringify({           
    raw: encodedResponse,
    threadId: "<THREAD_ID_OF_MESSAGE_TO_RESPOND_TO>"
  })
});

Solution 2

The answer of @Tholle (thanks!) was correct and put me on the right track, but after the recent changes:

https://gsuiteupdates.googleblog.com/2019/03/threading-changes-in-gmail-conversation-view.html

I had to conflate his two paths.

In my program I had to reply to a thread, but if I included only the threadId (as #2) the new message is put in thread by Gmail only in the mail of the replier, while in the mail of the original sender (also gmail) is appeared as a new thread.

I resolved by including both the threadId and the headers "References" and "In-Reply-To" with the id of the last message.

Comments

[Tholle]

Do you want to respond to a single message or respond to the thread?

[Vlas Bashynskyi]

I want to respond to a single message.

[vikramaditya234]

I tried the first solution given by you, but I am receiving 2 mails. One as a part of the mail thread and other is new. Second method fails with error "Invalid parameter". I am trying to add the draft to the thread, so far with no success. Google API documentation seems incorrect too.

[Tholle]

@vikramaditya234 You could try this.

[Tal Avissar]

what happens if my existing message that I want to reply to don't have the headers References/In-Reply-To ? stackoverflow.com/questions/44880439/…

[Andrey Tagaew]

Thank you for a great explanation and reference, it really helped me. Unfortunately first method is not working - i'm receiving separate email. However, once I added threadId as you suggesting in your second solution, I got email chain!

[zee]

@Tholle the workaround of passing 'ThreadID' in message object is not working anymore and the messages are not threaded. Is it because of new threading changes introduced by Google

[WtFudgE]

Passing the threadid into the message object works for me actually, the only issue with this one is that the subject won't get updated if i set a new subject, weird

[Gal Morad]

I wonder if the message is available by get immediately after sendMessage, or this is async process and the message is not immidialaty available. I am asking since I would like to save the message-id header in a database right after it was sent.