Very often users forgot to select "Reply" when answering to message, and sends new message as new "thread". For fix this they copy-paste message text, send as new "Reply" message, and delete original message.
For simplify this correction task, will be good to have ability for attach already sent message to other message as reply, via Edit form.
UI/UX suggestion on how to do this: When user is editing a message, clicking on a reply (currently does nothing while editing) makes the current message a reply.

We also need to think about disengaging a reply (accidentally replied, when meant to send a non-reply).
For this, while editing, an X button should appear on the reply (like on link previews).
Problem is, that X might be misinterpreted as 'cancel editing'. Instead of using the X icon, I'd use the symbol, but with something to indicate, that it's for unlinking (I have seen it before, there's something happening in the middle of the chain, a zap or something).
Related #2349 (If implementing this, consider that in the future, one should be able to move messages in and out of threads. Make it modular and make the next person's life easier.)
The best way to implement this is probably a 'hidden head tag', what says 'this message is attached to (reply of) message id x, in thread y'.
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Related #2349 (If implementing this, consider that in the future, one should be able to move messages in and out of threads. Make it modular and make the next person's life easier.)
The best way to implement this is probably a 'hidden head tag', what says 'this message is attached to (reply of) message id x, in thread y'.