Save Gmail Drafts with Google Apps Script

The Mail Merge Add-on uses the new Gmail API to create and save draft messages Gmail programmatically, something which cannot be done using the standard GmailApp or MailApp service of Google Apps Script. The Gmail API can create draft messages in rich-text which you can generate using the HTML Mail app.

You’ll have to enable the Gmail API under the Google Services console for this code to work.

// Credit:

function createHTMLDraftInGmail() {
  var forScope = GmailApp.getInboxUnreadCount(); // needed for auth scope
  var htmlBody = '<p>Hello, I am an HTML message</p><hr>';

  var raw =
    'From: Me <>\r\n' +
    'To: You <>\r\n' +
    'Subject: Save Draft Message\r\n' +
    'Content-Type: text/html; charset=UTF-8\r\n' +
    '\r\n' +

  var draftBody = Utilities.base64Encode(raw, Utilities.Charset.UTF_8).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('', params);
Amit Agarwal

Amit Agarwal

Google Developer Expert, Google Cloud Champion

Amit Agarwal is a Google Developer Expert in Google Workspace and Google Apps Script. He holds an engineering degree in Computer Science (I.I.T.) and is the first professional blogger in India.

Amit has developed several popular Google add-ons including Mail Merge for Gmail and Document Studio. Read more on Lifehacker and YourStory


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Digital Inspiration has won several awards since it's launch in 2004.

Google Developer Expert

Google Developer Expert

Google awarded us the Google Developer Expert award recogizing our work in Google Workspace.

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