Software for threaded conversations

[richard_wein]

Hi. I wonder if anyone could suggest a good method for handling threaded conversations with a client. A common situation is that a client sends me a list of topics to address,  I respond to each of them,  he responds to my responses,  and so on.  This may go on for a good few iterations. It would be useful to be able to do this in a way that makes it easy to review the discussion and see who was responding to what.

I recently used a Word document for this, with indentation and a new colour for each level of response. But there must be a better way. It would be great if it was also possible to collapse threads that are finished (but still be able to expand them again), and handle more than two participants. 

Any suggestions, please?