Gmail API: put email in draft and set "request Read Receipt" flag

Question

I made this tiny piece of .NET software that takes a PDF, splits it into pages and create several draft emails on Gmail using official APIs, ready to be checked and sent.

This is the method that takes a GmailService object and create the draft:

private void CreateDraft(GmailService gmailService, MailDraft mailDraft)
{
    var mailMessage = new System.Net.Mail.MailMessage();
    
    mailMessage.To.Add(mailDraft.Recipients);
    mailMessage.Subject = mailDraft.Subject;
    mailMessage.Body = mailDraft.Body + "\r\n" + mailDraft.Signature;

    foreach (System.Net.Mail.Attachment attachment in mailDraft.Attachments)
    {
        mailMessage.Attachments.Add(attachment);
    }

    var mimeMessage = MimeKit.MimeMessage.CreateFromMailMessage(mailMessage);

    // Add Read Receipt request
    if(mailDraft.RequestReadReceipt)
    {
        // Note that this is correctly filled
        Profile currentUserProfile = gmailService.Users.GetProfile("me").Execute();
        string currentUserEmail = currentUserProfile.EmailAddress;

        mimeMessage.Headers.Add("Disposition-Notification-To", currentUserEmail);
    }

    var draft = new Draft
    {
        Message = new Google.Apis.Gmail.v1.Data.Message {
            Raw = Encode(mimeMessage)
        }
    };

    Draft createdDraft = gmailService.Users.Drafts.Create(draft, "me").Execute();
}

internal class MailDraft
{
    public string Recipients { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }
    public string Signature { get; set; }

    public List<System.Net.Mail.Attachment> Attachments { get; set; }
    public bool RequestReadReceipt { get; set; }
}

As you can see in the code, I set an header in mimeMessage to request Read Receipt, this is the Disposition-Notification-To, with value equal to the current user email address.

Unfortunately, when I open the saved draft in Gmail, it has not the request Read Receipt set to on:

Note that this perfectly works if I send the email instead of saving it to draft (i.e. the read confirmation is requested on the other side).

Any idea?

Answer 1

When adding a custom MIME Header to the message and inserting it as a Draft using GMail API, it ends by stripping the additional header from the message.

I would recommend reporting it as a Feature Request in the Issue Tracker however there is one already opened requesting the same feature. You can check it here