Get the full whisper chat history

Is it possible to get all the whisper messages that you have exchanged with another person? For example if you have some extensiv whisper chats and you want to save the chat history in some textfile. My idea was a auto scroll macro for the mouse and then just copy and paste to a file. The problem is that I get a “Out of memory” error everytime I do this. So it seems that this method not works for extensive whisper chats. Is there a other way to get all the messages?

There is no History endpoints for chat and/or whispers.

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