We have an iOS app connected to an AppAngine backend and we have implemented basic emailing functionality using the GMail API (from the backend) however reply to still has a small problem: we noticed that the reply arrow is not shown in desktop email client (eg. Apple Mail app in my tests) when we reply from our app. (We have set the required headers (In-Reply-To and References) and the threadId, as described in the API docs, and the email was sent succesfuly)
Then we figured it out after reading (https://www.rfc-editor.org/rfc/rfc3501#section-2.3) and experimenting with IMAP using a local script:
- for marking the message as replied we had to set the \Answered flag; then the small arrow icon will be shown in email clients.
Is there any way to set the \Answered flag using the GMail API?