MIME标头无法通过Gmail API实现

Question

I'm trying to automate the creation of drafts via the Gmail API, and I want these drafts to be responses to existing emails. To do this, I believe I need to set the "threadId" header (Gmail specific), the "References" header, and the "In-Reply-To" header. Additionally, for Gmail to consider the message to be a reply, the "Subject" header must match the original email.

I'm hardcoding all of these headers into a MIMEText object, and then base-64 encoding (urlsafe) the message as a string and having the Gmail API deliver it. However, the "threadId", "In-Reply-To", and "References" headers don't appear to ever make it in the email that's sent, as they don't exist in the MIME shown when clicking "Show original" in the Gmail UI.

new = MIMEText("reply body text")
new["In-Reply-To"] = "[Message-ID of email to reply to]" #looks like <..@mail.gmail.com>
new["References"] = "[Message-ID of email to reply to]" #looks like <..@mail.gmail.com>
new["threadId"] = "[threadId of message to reply to]" #looks like 14ec476abbce3421
new["Subject"] = "Testsend2"
new["To"] = "[Email to send to]"
new["From"] = "[Email to send from]"

messageToDraft = {'raw': base64.urlsafe_b64encode(new.as_string())}
message = {'message': messageToDraft}
draft = service.users().drafts().create(userId="me", body=message).execute()

Answer 1

Actually, it's a lot simpler than that! If you just supply the correct Subject in the headers, and the correct threadId in the body, Google will calculate all the references for you.

new = MIMEText("This is the placeholder draft message text.")
new["Subject"] = "Example Mail"
new["To"] = "emtholin@gmail.com"
new["From"] = "emtholin@gmail.com"

raw = base64.urlsafe_b64encode(new.as_string())
message = {'message': {'raw': raw, 'threadId': "14ec598be7f25362"}}
draft = service.users().drafts().create(userId="me", body=message).execute()

This results in a draft, ready to be sent in the correct thread:

Then, I send the mail. As you can see, the references are calculated for you:

MIME-Version: 1.0
Received: by 10.28.130.132 with HTTP; Sat, 25 Jul 2015 07:54:12 -0700 (PDT)
In-Reply-To: <CADsZLRz5jWF5h=6Cs1F45QQOiFuqNGmMeb6St5e-tOj3stCNiA@mail.gmail.com>
References: <CADsZLRwmDZ_L5_zWqE8qOgoKuvRiRTWUopqssn4+XYGM_SKrfg@mail.gmail.com>
    <CADsZLRz5jWF5h=6Cs1F45QQOiFuqNGmMeb6St5e-tOj3stCNiA@mail.gmail.com>
Date: Sat, 25 Jul 2015 16:54:12 +0200
Delivered-To: emtholin@gmail.com
Message-ID: <CADsZLRxuyFhuGNPwjRrfFVQ0_2MxO=_jstjmsBGmAiwMEvfWSg@mail.gmail.com>
Subject: Example Mail
From: Emil Tholin <emtholin@gmail.com>
To: Emil Tholin <emtholin@gmail.com>
Content-Type: text/plain; charset=UTF-8

This is the placeholder draft message text.