Question

When providing the same subject line doesn’t work?

I’d like to send 2 emails and make them appear in one conversation. Sadly, the second one always starts a new conversation. How to avoid this?

Both mails are sent directly to [e-mail]

Both have almost the same headers and the same UTF-8 encoded subjects:

Delivered-To: [e-mail] Received: by ... Return-Path: ... Received: ... Received-SPF: pass ... Authentication-Results: mx.google.com; spf=pass ... Received: from mm_www by ... To: [e-mail] Subject: =?UTF-8?...=?= From: [e-mail] Content-Type: text/plain; charset=UTF-8; format=flowed MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Mailer: PHP Message-Id: ... (Different for both messages. Should I add my own id?) Date: ... 

Any clues?

Answer 1

Yes, the message ID is what’s important here. The client uses it to determine flow.