How to send a reply with attachment using Gmail API?

Other Questions Gmail
1

I’m trying to figure out how to reply to an email with an attachment using the Gmail API. I’ve got it working for new emails, but I’m stuck on replies.

When I try to add the threadId to my request, I get a 'Recipient address required.' error. Here’s what my code looks like:

function sendReply(threadId, attachment) {
  const payload = {
    raw: createEmailContent(),
    threadId: threadId
  };

  fetch('https://www.googleapis.com/upload/gmail/v1/users/me/messages/send?uploadType=multipart', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${getAccessToken()}`,
      'Content-Type': 'message/rfc822'
    },
    body: JSON.stringify(payload)
  })
  .then(response => response.json())
  .then(data => console.log('Success:', data))
  .catch(error => console.error('Error:', error));
}

Can anyone help me figure out what I’m doing wrong? I’m not sure why it’s asking for a recipient address when I’m trying to reply to an existing thread. Any tips would be really appreciated!

2

I’ve dealt with this issue before. The key is to include all necessary headers in your raw email content, even for replies. Make sure your createEmailContent() function sets the ‘To’, ‘Subject’, ‘In-Reply-To’, and ‘References’ headers. Also, double-check that you’re properly base64 encoding the entire message, including headers and attachments.

Another thing to watch out for is the Content-Type header. For multipart messages with attachments, it should be ‘multipart/mixed’, not ‘message/rfc822’. Lastly, ensure you’re using the correct endpoint for sending messages with attachments. The URL should be ‘https://gmail.googleapis.com/upload/gmail/v1/users/me/messages/send’ instead of the www subdomain.

If you’re still having trouble after these adjustments, consider using a library like nodemailer to handle the complex parts of MIME message creation.

3

I encountered a similar situation when working with the Gmail API. Even though you are replying to an existing email thread, the underlying email still requires complete header information, including the recipient address. I solved the issue by ensuring that my email creation function explicitly set the ‘To’ header along with the other necessary headers such as ‘In-Reply-To’ and ‘References’. In addition, I confirmed that the entire email, including its headers and attachments, was correctly encoded in base64. This approach made sure that the API had all of the information it needed to process the reply without errors.

4

hey there! i’ve run into this before. make sure ur createEmailContent() function includes the ‘To’ header, even for replies. also, double check ur base64 encoding - that tripped me up. oh, and the Content-Type should be ‘multipart/mixed’ for attachments. hope that helps!