inserting messages into existing threads

[jimhester]

This is possible with the threadId parameter in the API, however you have to set the References, In-Reply-To and Subject headers properly. It would be nice to make this automatic, i.e. by passing a function the thread object and the message, and have it modify it appropriately.

[mcomas]

How do you set the References, In-Reply-To and Subject headers properly with gmailr. I am trying to create a response for a specific message.