Hi, is it possible to thread using the Postmark plugin?
From Postmark:
Hello @jj11 ,
Thank you for reaching out to us.
Yes, it should be possible to send threaded messages using the Rich Postmark plugin. To do this, ensure that you maintain the same subject and recipient. Additionally, in the “Reply to” field, reference the last MessageID along with your email domain(img), such as “@example.com”. We will continue to review this functionality to ensure that everything is operating smoothly and will keep you updated on any developments.
In the meantime, please let us know how you are progressing with it or if you have any further questions about our plugins.
Thank you once again, and I look forward to your reply.
Best regards,
Stefan
Hi @jj11,
I hope this message finds you well. 
After thorough research, we’ve explored the possibility of fully integrating the API architecture allowing you to send messages in thread as you asked. I’m want to inform you that we’ve added this idea to our future roadmap for the plugin. And in case such improvement will be added we will le you know first.
Thank you once again for your valuable input.
Have a great week ahead!
Best regards,
Stefan