How to send the email from Google Apps Script using GMAIL API?

I am trying to automise sending of the Emails from my account using Gmail API in Google Apps Script.

Here is my code:

function email_checker() {
  var yourEmailAddress = "###@gmail.com";
  var myEmailAddress = "support@###.com";
  var subject = "testing mail";
  var forScope = GmailApp.getInboxUnreadCount();
  var htmlBody = '<html><body>' + '<h1>HI</h1>' + '</body></html>';

  var message = 'From: Me <' + myEmailAddress + '>\r\n' +
    'To: Me <' + myEmailAddress + '>\r\n' +
    'Subject: ' + subject + '\r\n' +
    'Content-Type: text/html; charset=utf-8\r\n' +
    'Content-Transfer-Encoding: quoted-printable\r\n\r\n' +
    htmlBody;

  var draftBody = Utilities.base64Encode(message);
  draftBody = draftBody.replace(/\//g, '_').replace(/\+/g, '-');

  var params = {
    method: "post",
    contentType: "application/json",
    headers: {
      "Authorization": "Bearer " + ScriptApp.getOAuthToken()
    },
    muteHttpExceptions: true,
    payload: JSON.stringify({
      "message": {
        "raw": draftBody
      }
    })
  };

  var resp = UrlFetchApp.fetch("https://gmail.googleapis.com/upload/gmail/v1/users/me/messages/send", params);
  Logger.log(resp.getContentText());
}

I am getting the following error: Media type 'application/json' is not supported.

Can anyone please advise on what I am doing wrong?

Thank you.

Solution

I believe your goal and your current situation as follows.

You want to send an email using Gmail API with UrlFetchApp.
You have already done the settings for sending the email.
- Gmail API is enabled.
- The scopes for sending emails can be included.

Modification points:

From your endtpoint, it is found that the media upload request is used.
In this case,
- the request body is required to create with multipart/alternative.
- It is not required to use the base64 encode with the web safe.
- The content type is required to use message/rfc822.
- The created request body can be directly used for payload.

When above points are reflected to your script, it becomes as follows.

Modified script:

function email_checker() {
  var yourEmailAddress = "###@gmail.com";
  var myEmailAddress = "support@###.com";
  var subject = "testing mail";
  var forScope = GmailApp.getInboxUnreadCount();
  var htmlBody = '<html><body>' + '<h1>HI</h1>' + '</body></html>';

  var message = 'MIME-Version: 1.0\r\n' +
    'From: Me <' + myEmailAddress + '>\r\n' +
    'To: Me <' + myEmailAddress + '>\r\n' +
    'Subject: ' + subject + '\r\n' +
    'Content-type: multipart/alternative; boundary=boundaryboundary\r\n\r\n' +
    '--boundaryboundary\r\n' +
    'Content-type: text/html; charset=UTF-8\r\n' +
    'Content-Transfer-Encoding: quoted-printable\r\n\r\n' +
    htmlBody + "\r\n\r\n" +
    '--boundaryboundary--';

  var params = {
    method: "post",
    contentType: "message/rfc822",
    headers: {
      "Authorization": "Bearer " + ScriptApp.getOAuthToken()
    },
    muteHttpExceptions: true,
    payload: message
  };

  var resp = UrlFetchApp.fetch("https://gmail.googleapis.com/upload/gmail/v1/users/me/messages/send", params);
  Logger.log(resp.getContentText());
}

Note:

If you want to use the endpoint of POST https://gmail.googleapis.com/gmail/v1/users/{userId}/messages/send, please modify your script as follows.

From

  var params = {
    method: "post",
    contentType: "application/json",
    headers: {
      "Authorization": "Bearer " + ScriptApp.getOAuthToken()
    },
    muteHttpExceptions: true,
    payload: JSON.stringify({
      "message": {
        "raw": draftBody
      }
    })
  };

  var resp = UrlFetchApp.fetch("https://gmail.googleapis.com/upload/gmail/v1/users/me/messages/send", params);
  Logger.log(resp.getContentText());

  var params = {
    method: "post",
    contentType: "application/json",
    headers: {
      "Authorization": "Bearer " + ScriptApp.getOAuthToken()
    },
    muteHttpExceptions: true,
    payload: JSON.stringify({"raw": draftBody})
  };

  var resp = UrlFetchApp.fetch("https://gmail.googleapis.com/gmail/v1/users/me/messages/send", params);
  Logger.log(resp.getContentText());

In this case, var draftBody = Utilities.base64Encode(message); draftBody = draftBody.replace(/\//g, '_').replace(/\+/g, '-'); can be also modified to var draftBody = Utilities.base64EncodeWebSafe(message);.

Reference:

Method: users.messages.send