GmailApp – Add label to specific message, not the thread
You can do this using the GMail API instead. You need to enable the API for your project. In the editor, select Resources > Advanced Google services, then click on “These services must also be enabled in the Google Developers Console.” There, enable the GMail API. modifyMessage Example of use: modifyMessage(‘me’, messageId, [‘stack’,’overflow’]); // add … Read more