I've develop webmail client for any mail server.
I want to implement message conversion for it — for example same emails fwd/reply/reply2all should be shown together like gmail does... 
My question is: what's the key to find those emails which are either reply/fwd or related to the original mail....
The In-Reply-To header of the child should have the value of the Message-Id header of the parent(s).
How to maintain mail conversion (reply / forward / reply to all like gmail) of email using Python pop/imap lib?