How to have forward messages appear in the same thread with Gmail API

Question

I am trying to have forward appear in the same thread when sending message with gmail API (which gmail/inbox is doing perfectly fine from the UI).

This is working fine when I reply (I am adding the threadId, the 'Re: ' and using the RFC 2822 convention (with 'In_Reply_To' and 'References' headers)) but when I try to forward a message from a thread (the only difference with previously is that I put 'Fwd: ' instead of 'Re: ' in front of the subject) it will appear outside of the thread on the gmail UI.

What am I doing wrong? How does google keep forwarded message in the same thread? (I am working with the Python API if this is of any help)

Thanks a lot,

Answer 1

Gmail Help - Change how you see reply emails says that a conversation breaks off into a new thread if the subject line changes or the conversation reaches more than 100 messages.

It also gives out in Forward messages that forwarding an individual message is different from forwarding an entire conversation. Steps are given as shown below:

Forward an individual message

1. Open the message you want to forward.
2. Click the Forward link in the box below the message. If you don’t see the Forward link, click the down arrow next to Reply in the top-right corner of the message and select Forward.
3. Add the new recipient(s) and any additional text to your message.
4. Click Send.

Forward an entire conversation

1. Open the conversation.

2. Click the More button in the toolbar above your messages and select Forward all.

In additon to that, I found a post by Senseful Solutions - How does email threading work in Gmail?. It gives out that the following rules must be met:

1. The subject must be similar.
2. The sender must be a part of the thread OR in-reply-to must be used.

I hope I was able to help. :)